Slow Cooker French Onion Soup
34 CommentsUpdated Jan 28, 2026
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Make a cozy batch of French Onion Soup with deeply caramelized onions, rich broth, and simple seasonings. Just before serving, it’s finished with toasted bread and melted cheese for that classic, comforting touch.
Crockpot French Onion Soup brings restaurant-quality flavor right to your kitchen! Unlike traditional versions that can taste like plain beef broth and onions, my recipe is elevated with butter, balsamic vinegar, and a blend of spices for incredible depth. Plus, don’t miss my tips for perfect croutons to serve under the melted cheese.
What You’ll Need
Onions: Sweet yellow onions are best, but white or red will work in a pinch.
Butter & Flour: Used to caramelize the onions and thicken the broth slightly.
Beef Broth: Go with a good-quality broth or stock for a rich, deep flavor.
Seasonings: Garlic, thyme, oregano, Worcestershire, and a splash of balsamic vinegar for balance.
Optional Sugar: Just a bit, only if your onions aren’t labeled “sweet.”
Toppings: Baguette slices, olive oil, garlic, Swiss or provolone cheese, and a little parmesan for that classic finish.
A Large Crockpot
How to Make French Onion Soup in the Crockpot
Start by cooking the onions in butter until deeply golden and soft, then stir in flour to thicken. Transfer everything to the slow cooker with broth, seasonings, and a splash of vinegar. Let it cook low and slow until the flavors come together. Just before serving, toast baguette slices, melt cheese over the top, and ladle the soup into bowls. (Find the Full Recipe in the Recipe Card).
Best Cheeses for French Onion Soup:
Here are the top cheeses to use, though you can use any you have on hand.
- Gruyère – the classic choice with a rich, nutty flavor
- Swiss or Baby Swiss – mild and melty
- Mozzarella – for a gooey, stretchy topping
- Parmesan – great for sprinkling on top for extra flavor (use along with one of the melty cheeses)
What Can be used instead of bread?
- Store-bought croutons – Yes! This works well. When I worked at Marie Callender’s, they used bagged croutons for their French Onion Soup.
- Garlic bread or French Bread – Cut a loaf of store-bought garlic bread or French bread into cubes. Broil until crisp and browned.
- Stove-top stuffing – You can add a sprinkle of stove top stuffing, it will soak up some of the soup and give you a base to put your cheese.
Featured Comment
“This might possibly be the best recipe for French Onion soup I have ever made! Easy to prepare, full of flavor and perfect for a cold Winter’s day! This is definitely a keeper!”
– pam
More French Onion Style Recipes
French Onion Chicken is simmered with caramelized onions and melty cheese for a cozy main dish.
French Onion Pot Roast cooks low and slow in rich broth with sweet onions.
For a quick snack, try French Onion Dip made with sour cream and Lipton onion soup mix.
Slow Cooker French Onion Soup Recipe
How to Video
Ingredients
- 1 stick butter
- 5 sweet yellow onions, sliced (white, yellow or red onions work too)
- 1 tsp. salt
- 1/4 tsp. pepper
- 1/4 cup flour
- 64 oz. beef broth or beef stock, (two 32-oz. containers)
- 1 tsp. sugar (optional), I only use this if my onions aren't labeled "sweet onions"
- 2 tsp. minced garlic
- 1/4 tsp. dried thyme (not ground)
- 1/4 tsp. dried oregano (not ground)
- 1 tsp. Worcestershire sauce
- 1 Tbsp. balsamic vinegar
- 1 bay leaf
For serving (not included in nutritional count)
- 1 baguette
- olive oil
- 1 whole garlic clove
- sliced swiss cheese (can use provolone or gruyere), (about 2 slices needed per serving)
- shredded parmesan cheese, (use about 1 tablespoon per serving)
Instructions
- In a large skillet set to medium high heat, add the butter. When the butter is melted add the sliced onions. Sprinkle with the salt and pepper.
- Saute the onion until browned and caramelized. This will take about 10 minutes. Stir often. Adjust the heat if they start to burn.
- When the onions are done cooking add the flour to the butter and onions. Cook for 2 more minutes.
- Add the floured onions to the slow cooker. Add the beef broth, sugar (if using), garlic, thyme, oregano, Worcestershire sauce, and balsamic vinegar. Stir well. Add the bay leaf on top.
- Cook on HIGH for 4 hours or LOW for 8 hours.
- Remove bay leaf before serving.
How to make the homemade croutons:
- Preheat the oven to 500 degrees (broil).
- Cut a baguette into 1/4 inch slices. Place slices on a sheet pan.
- Using a pastry brush, brush olive oil onto the slices.
- Place the sheet pan under the broiler. Cook for about 3-5 minutes or until browned and toasty.
- Cut a garlic clove tip off and rub each piece of cooked bread with it. This will give the bread garlic flavor.
How to assemble the bowls of soup:
- Fill an ovenproof bowl with the French Onion Soup broth. Place the bowl in a pie tin or on a sheet pan. (You can make more than one bowl at a time).
- Add the homemade croutons (or store-bought) on top of the soup.
- Place 1-2 pieces of swiss cheese (can use provolone or gruyere) and sprinkle on parmesan cheese.
- Broil until the cheese starts to brown and is bubbly.
Sarah’s Notes
Nutrition
Nutrition info is auto-generated. This information is an estimate; if you are on a special diet, please use your own calculations.
More Slow Cooker Soup Recipes
Warm up with hearty favorites like Stuffed Pepper Soup, Slow Cooker Broccoli Cheese Soup, and Baked Potato Soup—all rich, filling, and full of flavor.
For something classic, try Slow Cooker Chicken Noodle Soup or Slow Cooker Tomato Soup, perfect for a cozy night in.
You can also enjoy Corned Beef and Cabbage Soup, Ham and Beans, or creamy Turkey Chowder for a comforting twist on traditional leftovers.
I love French onion soup so I was excited to try this for a first time making and I am upset with the outcome. In my opinion, this doesn’t taste like French onion, or anything really. Lack of flavor, very light in color. Maybe I did something wrong but won’t be trying this recipe again
I’ve had mine on high for several hours now and it’s finally starting to cook down; not no 4 hours!! And mine is horribly bitter for some reason..
This was amazing!! I did make this GF with no problem or sacrificing flavor by using gluten free 1-1 flour and gluten free soy sauce instead of Worcestershire sauce but I omitted the additional salt due to using soy because of the salt content. I also substituted 1/2 tsp Italian seasoning for the dried thyme and oregano just because I didn’t have any separates. For GF reasons, to make the bread topper, use a slightly denser/thicker sliced GF bread so it will hold up to the moisture of the steaming broth and a GF cheese option.
Can you cook the onions the night before and put it in the crockpot the next day
Yes!
To save the time in caramelizing onions on the stove top you can actually make them right in the crock pot. The day before you can load up the crock pot with thinly sliced onions and set it to low all day / 8 to 10 hours and it should not need to be stirred.
Either that same day or the next day add all the other ingredients and let it simmer for an hour. Easy Peasy . .
Did the onions caramelize nicely? Butter? No stirring?
Excellent recipe! I specifically searched for a crock-pot version, and husband loves it!
I thought it looked anemic, so I added a tablespoon of Kitchen Bouquet for deeper color..and 2 beef bullion cubes for more flavor..yummy!
Just made this tonight, delish, it’s a keeper.
Easy, nurishishing & delicious. This recipe got me through when I had Covid & I have eaten it almost everyday as I recover.
Best french onion soup I have ever made!!!!
A lot of French Onion Soups have red wine in them. Can this be incorporated into this recipe?
Yes, I would use about a cup of wine in place of some of the broth.
How did the wine replacing the broth change the flavor?
If you want to use wine only use a spalsh to 1/4 cup it can be strong if any more is used.
Great soup! Thanks for the recipe!
Can I use Vegetable Broth
yes