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!
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Reasons to make slow cooker french onion soup
- So easy. This French onion soup is ridiculously easy to whip up with so much hands-off cooking thanks to the crockpot.
- No babysitting caramelized onions. No one, and I really do mean no one, is babysitting the caramelized onions here. Nope. We’re throwing them all in the crockpot and letting it do all the heavy lifting for us.
- Cozy, hug-in-a-bowl vibes. This soup is oh-so-perfect for a chilly, blustery snow day, keeping you warm and cozy all day long from the inside out.
- Freezer-friendly. French onion soup is a great recipe to freeze for later, allowing for easy thawing and reheating for those super busy weeknights.
what is french onion soup
French onion soup originated in France in the 18th century – a common staple as onions were plentiful, cheap and easy to grow. It is a soup of caramelized onions typically cooked in beef stock, topped with bread and cheese.
tips and tricks for success
- Use sweet onions. Although most recipes call for yellow onions, sweet onions allow for deeper caramelization, resulting in a more rich, pleasant sweetness to the soup.
- Use good-quality stock. The better quality your stock, the better your soup. Many brands love to pack in the salt so always opt for unsalted or a lower-sodium variety.
- Gruyere cheese is key. Gruyere is traditionally used in French onion soup for its rich, nutty flavors and great melting capabilities.
- Use oven-safe bowls. Ramekins, great for individual servings, can withstand high heat under a broiler.
- Freeze as needed. French onion soup is very freezer friendly. Freeze without the baguette slices and cheeses, and store up to 3 months.
what to serve with french onion soup
Slow Cooker French Onion Soup: Frequently Asked Questions
Absolutely! But because dried herbs are often more potent/concentrated than fresh herbs, you need less when using dry. The correct ratio is 1 tablespoon fresh herbs to 1 teaspoon dried herbs.
You can substitute the sherry vinegar with white wine, dry vermouth, apple cider vinegar or rice wine vinegar.
Swiss cheese or fontina cheese are suitable alternatives.
We highly recommend a baguette or other crusty French bread.
No crockpot, no problem! We have a stovetop recipe here.
Leftovers can be stored in an airtight container in the fridge for 3-4 days, storing separately from the baguette slices and cheese.
Absolutely! Let cool completely; portion into plastic freezer bags in individual servings, squeezing out any excess air before sealing. Lay the bags flat in a single layer in the freezer (this will help them freeze quickly). To reheat, thaw overnight in the fridge, reheating over low heat, stirring occasionally, until heated through. When ready to serve, add your baguette slices and cheeses!
Slow Cooker French Onion Soup
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
Equipment
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.
Video
Notes
Did you make this recipe?
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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.
Awesome goodness! 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.
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. 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!
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!
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.
That’s great!
Do you think that this would freeze well in individual portions?
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.
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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!
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!