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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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 .
I actually make it the day before to serve as I find it has a richer flavour. I’ve even frozen it with excellent results.
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. I wish I had some cooking in the oven as I type. 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.
I actually don’t have a preferred brand!
Should this be salted or unsalted beef stock?