Damn Delicious

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!

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!

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!

15 minutes10 hours 5 minutes

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 (12-ounce) French baguette, sliced
  • 1 cup shredded Gruyère cheese
  • 1 cup shredded asiago cheese

Directions:

  1. Place onions into a 6-qt slow cooker.
  2. 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.*
  3. 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.
  4. Preheat oven to broil.
  5. 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.
  6. 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.
  7. Serve immediately.

Notes:

Stir halfway, as needed, to prevent burning.

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70 comments

  1. 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.

  2. Should this be salted or unsalted beef stock?

  3. Rated 5 out of 5

    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!  

  4. 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?

  5. Rated 4 out of 5

    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! 

  6. Rated 4 out of 5

    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.

  7. Rated 4 out of 5

    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.

  8. Rated 1 out of 5

    Put stuff in at 9pm, woke up at 8 am to a blacker than black pot of onions, and a ruined crock pot. Not sure we’ll ever try again.

    • Steve, I’m so sorry this happened to you but we specifically state in the directions to let the onions cook for 8-10 hours and to stir halfway, as needed, to prevent burning. With 11 hours of cook time without any kind of stirring, the onions will burn without a doubt.

      We hope you get to try this again as written. 🙂

  9. Rated 5 out of 5

    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!

  10. Rated 5 out of 5

    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!

  11. Rated 5 out of 5

    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!

  12. 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. 

  13. Do you think that this would freeze well in individual portions? 

  14. 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.

  15. 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! 

  16. Can you skip the bread on top?

  17. 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!

  18. 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!

  19. 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! 

  20. Can this recipe be cooked in the Instant Pot?

    • Unfortunately, without further recipe testing, I cannot answer with certainty. As always, please use your best judgment regarding substitutions and modifications.

  21. I’m seeing a lot of liquid in with my onions. Should I strain it off to help them caramelize?

  22. 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!

  23. Could you use vegetable broth instead of beef?

    • 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 ….

  24. 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!

  25. 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 .

  26. 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?

  27. 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!

  28. 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.!

  29. This looks absolutely delicious.  I wish I had some cooking in the oven as I type.  Yum!

  30. 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?

  31. 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!

  32. 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?

  33. 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!

  34. 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! (:

  35. Is it really high heat for 8-10 hours? That seems like a long time to me at a high temperature.

  36. 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

  37. Is there a replacement for the sherry vinegar?

  38. 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.