Slow Cooker French Onion Soup
27 Comments Apr 15, 2024
Updated May 30, 2025
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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 like this recipe for some reason it was very peppery for me so going to remake it without any pepper now does anyone know a way to thicken it up a little (mine was runny I did the 4h on hight one but I am going to make the 8h on low tomorrow
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!
I adjusted and made a smaller amount to fit my 2 quart but it was only about half full – why use a 5 quart?
This post is exactly what I was looking for. You’ve addressed all the questions I had and provided clear, actionable advice.
Is there a way to make this using chicken or vegetable broth/stock and dairy free butter? I love this soup but can no longer eat mammalian meat or dairy (Alpha Gal allergy)
Thanks!
I don’t see why not! Dairy free butter actually tastes really good!
This is the third time I’ve made this soup and it gets better every time. I think mostly because I’m taking the time to cook the onions slowly, and completely; thus an hour prep not 25 minutes, but it’s worth the time because it’s delicious! Rich and hearty! We love it! Thank you.
I’m curious. How can 2 people make the same recipe and come out with 2 different opinions of the same recipe? Both seem to follow the recipe exactly. I want to make this soup., but, want it to turn out yummy.
Took the advice of another poster and just “caramelized” my onions in the crock pot the night before with the sugar.
Terrible recipe. Taste nothing like french onion soup. Never would thicken properly.
Of course you had to post negative as an anonymous person…
Amazing flavours! Thank you for this recipe.