Slow Cooker French Onion Soup
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Did you know you can make French onion soup in the crockpot?! It’s ridiculously easy with basically no stirring and no work!
It’s finally Fall. I mean, it’s been Fall for weeks but, it’s finally a little bit cooler in LA.
And when I say cooler, I mean 75 degrees.
That’s basically sweater and scarf weather for us. And French onion soup season.
Except, no one is babysitting the caramelized onions here. Nope. We’re throwing them all in the crockpot, and letting it do all the work for us.
All we do is add our bread slices and cheese. Then we broil the crap out of it until golden brown.
Slow Cooker French Onion Soup
Did you know you can make French onion soup in the crockpot?! It's ridiculously easy with basically no stirring and no work!
Ingredients
- 3 pounds sweet onions, thinly sliced
- 3 tablespoons unsalted butter, melted
- 2 teaspoons brown sugar
- Kosher salt and freshly ground black pepper, to taste
- 6 sprigs fresh thyme
- 1 bay leaf
- 6 cups beef stock
- 2 teaspoons sherry vinegar
- 1 French baguette, sliced
- 1 cup shredded Gruyère cheese
- 1 cup shredded asiago cheese
Instructions
- Place onions into a 6-qt slow cooker.
- Stir in butter, brown sugar and 1 teaspoon salt; top with thyme and bay leaf. Cover and cook on high heat for 8-10 hours, or until onions are caramelized and browned.*
- Stir in beef stock and sherry; season with salt and pepper, to taste. Cover and cook on high heat for 2-3 hours, or until heated through. Remove and discard thyme and bay leaf.
- Preheat oven to broil.
- Place baguette slices onto a baking sheet. Place into oven and broil until golden brown on both sides, about 1-2 minutes per side; set aside.
- Divide soup into ramekins or ovenproof bowls. Place onto a baking sheet. Top with baguette slices to cover the surface of the soup completely; sprinkle with cheeses.
- Place into oven and broil until golden brown and cheeses have melted; about 2 minutes.
- Serve immediately.
Notes
Stir halfway, as needed, to prevent burning.
Did you make this recipe?
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Fantastic soup! Â I exactly followed the directions and was so impressed with the delicious taste and ease of making it. Â
So, for some crockpots, high is too much for 8-10 hours. I had crispy and burnt onions around the sides of mine after 3 hours. Some damage control and dropping to low resulted in beautiful dark onions after 8 hours. The rest of the recipe is quite good.
Do we cut up the onions or just put the whole onions in the pot?
This was phenomenal! I caramelized my onions in a pot with the butter and brown sugar then put my beef broth and sherry vinegar and brought is all to a boil then transferred it to a hot crock pot. Cooked for about 4 hours and it was delicious! As for the cheese I broiled it on parchment paper until golden and laid it over the top.Â
#damndeliciousÂ
Can vegetable broth be used?
Would the flavor change much? Thank You.
An excellent french onion soup. Very easy to make and trouble free. Followed directions as written and worked out perfect. The rest of the readers should do the same and stop questioning you. Thanks so much for posting, its a keeper for sure
My favorite cozy fall meal.Â
This is a go-to recipe. Absolutely love it. I’ve also used the first part of the recipe, caramelizing the onions, and then put them in small baggies to freeze for ease when I need caramelized onions. Perfect. Thank you!
i HAVE MADE THIS TWICE AND THE SECOND TIME WAS EVEN BETTER. LOVE HOW EASY. GREAT WAY TO USE UP THOSE EXTRA ONIONS. USED FRESH ROSEMARY FROM THE GARDEN AND IT WAS DELICIOUS.
This is a HUGE hit in my house. I’ve made it several times and I get compliments. Vidalia onions work very well. But I’ve used yellow and white onions with tremendous success. Also, be sure to use fresh thyme as it makes a big difference.
Thank you for another great recipe.
DELICIOUS!! Love this recipe!
Can sherry cooking wine be subbed for the sherry vinegar?
Thanks!
Evidently you can combine red vinegar with sherry: 3:1 ratio and get a good substitute.
wondering about onions in soup that will be frozen as I’m cooking for one. Will the onions go bad faster when frozen and thawed, then other vegetables and legumes.?
Ohmigosh!  Best soup ever!  The sherry vinegar makes all the difference. Don’t substitute. Gave some to 3 friends and they confirmed it was awesome!  Thank u for the fabulous recipe.
Many thanks Chungah ….Enjoyed this easy recipe and yes, as asked by one of your fans, I made it in a multicooker on the slow cooker setting. I do not own a crock pot/slow cooker and it worked out really well. As with any type of cooking, keep an eye on your pot and adjust time if necessar. The recipe took a considerably shorter time to cook. I started off on high and changed to low setting. I did not have any dried or fresh herb seasonings other than some italian seasoning so that is what I used. I try not to stress when adapting a recipe..whats the worst that can happen? I also added 3 cloves of garlic…love that stuff and used sliced swiss cheese because that’s what was in the fridge. That is half the fun, experimentation! Again many thanks for giving me ideas for variations Chungah.
Has anyone made this with an InstaPot-like multiicooker?  The reason I ask, with most Crock-Pot type cookers  their heating elements are around the sides … where the heating elements of multi-cookers  are on bottom.  Just concerned about burning because of this difference.
Like you, I love French Onion Soup when it is a little cooler outside. I live in Florida so that means December through February. This soup is tasty and I would give it a 5 star but, I can’t say I wanted to wait for 13 hours for the soup to be ready. Yes, it’s pretty much hands off but, the timing for it. That was the reason for 4 stars instead of 5. Is there a way to shorten the time some like Cooking the onions on the stove or Instant pot and then placing in the Slow cooker? I would love to hear what you have to say about it. You have a lovely site and very cute doggies. Love their outfits! But Chicago???
Are you really on a recipe for a slow cooker and are dropping stars/surprised it cooked slow? For a slow cooker recipe? …If you don’t want it to cook slowly don’t use a recipe made for a slow cooker. That’s literally the point of this recipe lol. There are plenty recipes for French Onion Soup that uses the stove and oven….
Well to be fair… 13 hours is  a reeeealy long time, even for a slow cooker.  You’d have to get up at 5am to start it for it to be ready by supper time lol. Although my slow cooker tends to cook hot so it prob Wouldn’t take nearly that long.Â
Awesome goodness! Â This was so easy. After adding the melted butter to the onions in the crockpot I made sure the onions were all coated with the Butter. It was even better the next day.Â
This recipe states to cook on high, which has to be an error. I cooked mine on low and after 2 1/2 hours onions around the edge started to burn.
They are supposed to be really brown – I make this several times a year and don’t stir at all and nothing burns – on high for 8 hours. Â It might look burnt but it’s not and absolutely delicious!
Should this be salted or unsalted beef stock?
Sooooo good and so easy to make! I let the onions cook while I was at work and they were perfect by the time I got home! The bread on top melts perfectly into the soup. A must try! Â
I have a question. If I wanted to cook the onions tonight overnight and eat this for dinner tomorrow, could I add the broth and keep it on low or warm tomorrow? Or will it cook to much? What do you suggest if the onions are cooked ahead of time?
What a great idea! But unfortunately, without having tried this myself, I cannot answer with certainty. But if you get a chance to try it, please let me know how it turns out! Good luck! 🙂
I have a recipe for slow cooker onion soup that is very similar to this one. However, in mine, the onions are put in the crockpot with the butter and olive oil and cooked on low overnight. In the morning, you will have perfectly caramelized onions. I always do about 5 lbs and put the extra aside. You house will smell like caramelized onions as well….which I think is fabulous.
It took every bit of 10 hrs to bring the onions to the correct stage. They never dried out, were moist throughout. At 10 hrs. I added abt 2T of flour to help thicken broth and let that sit on high for another 1/2 hr. Then added stock Better than Bullion with a little red wine that was on hand instead of sherry vinegar. 3 hrs later. Delish. I’ve made this on the stove top many times, similar recipe, and it required lots of attention. All said, I think I prefer stove top,  but this was really good too. Low maintenance if you trust the recipe!Â
I used Bone Broth. Much richer beef flavor. Pacific brand is my goto. I used two tablespoons red wine along with the sherry vinegar. Delicious.
I was skeptical when I first saw this recipe. Then I tried it. So easy and the final product is actually French Onion soup as advertised. Delicious and a time saver. Lovely slow cooker blend of flavors, that mahogany color we all look for. The vinegar adds that extra taste found in all the best recipes. A family favorite.
I used yellow onions and dried thyme in a tea ball. Onions came out perfect in the morning then I threw in 4 eye of round steaks with the rest of the ingredients and 8 hrs on low. Used as base for Beef Stroganoff-delicious and cheaper than the cans of french Onion soup I used to use!
That’s so great! Thanks for sharing that with us, Kathryn!
I usually use Concentrated French Onion Canned Soup for my Beef Stroganoff. But I Made THIS! Yellow onions-Put Eye Of Round (on sale for$2.98/lb) and Dried Thyme in a Tea Ball in crock pot. 4 dinners worth with Noodles! Delicious!
Awesome soup!  It’s my favorite and I’ve never made it because I always thought it was too complicated  the crockpot made it so easy this recipe is a keeper!
The slow cooker makes life so much easier, right? 🙂
Love this recipe! Delicious and so easy. I put the onion mixture on before bed the night before. The next day I do the rest. Serving for a dinner party tonight!
Easy cleanup… I just soak my crock pot in hot water for a bit and then throw it in the dishwasher.Â
That’s great!
Do you think that this would freeze well in individual portions?Â
Freezing sounds like an amazing idea but unfortunately, I cannot answer this with certainty as I have never tried freezing this myself. Please use your best judgment for freezing and reheating.
Unfortunately, the crockpot method retains the moisture in the onions to the extent that no fond is formed. Therefore, we’re losing the most important technique to flavor the soup. Check this method: easy, no fuss and makes a glorious soup.
.
loshttps://www.geniuskitchen.com/recipe/french-onion-soup-the-cooks-illustrated-way-344164?ftab=reviewsing
Sorry Chungah, like your site & recipes but this did not work for me.
I thought the same thing when I made this because I like the caramelized flavor the fond adds, so I followed the recipe leaving one onion out, then I sauteed that onion in a pan to develop a fond, deglazed with red wine and threw it all in at the broth stage. DELICIOUS!!! And still easier.
That’s great!
Making it right now…can’t wait. Do you stir the onions at all during the 8hrs?! I’m worried the bottom will be more caramelized or burnt than the rest? Thanks. Love all your recipes!Â
No need to stir – that’s the beauty of the slow cooker! 🙂
Can you skip the bread on top?
Yes, of course.
Is it still french onion without the french bagette????
I cooked mine, added broth/stock & waited until next day to finish & it worked great! I had no sherry vinegar so used red wine & mozzarella/asiago/parmesan blend of cheeses & it was delicious. I doubled the recipe so I have enough to share. Delicious!
I cooked mine, added broth/stock & waited until next day to finish & it worked great! I had no sherry vinegar so used red wine & mozzarella/asiago/parmesan blend of cheeses & it was delicious. I doubled the recipe so I have enough to share. Delicious!
Making this right now, and to be honest I’m actually floored that these onions are not even the slightest bit burnt. To avoid having to wake up at the crack of dawn to make this, I put the onions in the crock pot and left them on low overnight and when I woke up hours later BAM. They look perfect! I know typically when you do low instead of high you double your hours (I’m doing 16), but according to my timer I’ve got 5 more hours left and they already look scrumptious. Looking forward to the finished product! Just letting some know that it can be done overnight!Â
Can this recipe be cooked in the Instant Pot?
I’m seeing a lot of liquid in with my onions. Should I strain it off to help them caramelize?
It should still be fine.
I made this last night/this morning and it’s some of the best French Onion Soup I’ve ever had. The only tweaks were I used red wine vinegar instead of sherry (didn’t have any,) and I went traditional with Swiss cheese. I can’t believe how good it is! I let the onions go for 8 hours on high, then added the broth and cooked that for 6 hours on low. I will make this at least once a week, most likely!
Could you use vegetable broth instead of beef?
Yes.
I get it we substitute while cooking sometimes as well, but again should we call this swiss onion as long as not using french cheese, we will and usually cook as directed the first time , “old man check” comes at midnight so we will be at thegrocery store ….
Love the recipe! I have an Instant Pot but no crock pot. Any idea how to adjust the cooking times / directions to make this soup? Thanks!
Unfortunately, without further recipe testing, I cannot answer with certainty. As always, please use your best judgment regarding substitutions and modifications. Sorry, Ally!
HI Ally, Is your Instant Pot also a slow Cooker?? I have the Instate Pot duo with air fryer 8 quart. Just asking.
Could you carmelize the onions the day before you want to serve it and put them in the refrigerator? The next day, bring the onions to room temperature, add the remaining ingredients and finish cooking?
Unfortunately, without further recipe testing, I cannot answer with certainty. As always, please use your best judgment regarding substitutions and modifications.
Yes. Start the onions the night before, cook all night, turn off if carmelized to your satisfaction, then finish when ready. I don’t even refrig, That’s me. Depending on your slow cooker, I might start on hi and switch to low for the night. I also put a piece of wax paper under the lid to keep a tighter .
Silly question perhaps, and I know French Onion soup is tricky to eat politely in the best of circumstances, but how exactly do you eat the baguette on top?
That does get tricky! I usually use mine as sort of a dipper and just eat it with my hands haha. Not the politest, but it does the job and is delicious!
I’m the same way. The dipper is the way to do it for sure!
I’ve never made soup on a slow cooker before, so I must say I’m really eager to try it after seeing these pics. Can’t wait!
thank you for adapting this for a slow cooker, I never think to make a lot of things other than roasts, or similar thick meats with a slow cooker, but why not? Nice not to have to keep stirring, etc.!
This looks absolutely delicious. Â I wish I had some cooking in the oven as I type. Â Yum!
My slow cooker manual says it must be 3/4’s full before turning it on. That would not be the case here until the beef broth is added?
Do you think that using a crockpot liner would affect the onion browning process? I adore my crockpot, but I can’t stand the cleaning after so my recipes live and die by whether or not I can use a liner. Thank you for this!
What a great idea! I love a crockpot liner – it truly makes my life so much easier. But I honestly have not tried it with this recipe so it’s hard for me to say with certainty. Sorry!
Mandy
I think you should experiment and tell us how it because I had the exact same question!!
Dave
I have never used a crockpot liner but I always spray my crockpot with oil before putting anything in it, and I’ve never had a problem with stuff sticking. It really does help.  Looking forward to trying this recipe!
Hi
I’m not sure about your total time for this recipe. You said total time is 10 hours and 20 min. But if the onions first take 8-10 hours and then we have to add in the broth, etc, and cook another 2-3 hours we’re looking at *potentially* 13 hours.
When does have to get started in order to have dinner at a reasonable time?
If the onions take 8 hours, and you cook an additional 2 hours with the broth, that is at least 10 hours.
That doesn’t really answer the reader’s question. Your directions say “8-10 hours”, so if they take 10 hrs to cook, then an additional “2-3 hours”, you’re looking at 10-13 hrs total. I was all for making this recipe until I saw the LONG time it will take.
Karen, if this recipe takes too long for you (8-10 hours which are idle), you can try this stovetop version instead. 🙂
This soup is absolutely wonderful. I only had 1 sweet onion so I added a red onion. That is the only change. My husband will ask for this often!
I think that is an awesome idea to use a slow cooker for this dish. Slowly letting the flavoured infuse in the soup. Love it! (:
Is it really high heat for 8-10 hours? That seems like a long time to me at a high temperature.
Yes, that is correct!
High heat in a slow cooker is not the same as high heat on a stove.
Thank you, thank you, thank you, for a recipe where one does not have to babysit the onions!
Can’t wait to make this recipe!
Theresa
It’s the best, right?!
Is there a replacement for the sherry vinegar?
Here is a great list of possible substitutes – hope that helps!
http://www.myrecipes.com/how-to/cooking-questions/sherry-vinegar-substitute
What an inventive recipe! Do you have a favourite brand of beef stock? I haven’t been able to find anything at the store with really good beefy flavour.Â
I actually don’t have a preferred brand!
Should this be salted or unsalted beef stock?