Make Slow Cooker French Onion Soup in your slow cooker. It has a rich buttery onion broth that is great with homemade croutons and cheese broiled on top.
It’s soup season (actually, every season is soup season for me). My family also enjoys baked potato soup and ham and bean soup.
Crockpot French Onion Soup is just as good as any fancy restaurant. My version doesn’t just taste like beef broth and onions. I add butter, balsamic vinegar, and spices, so the soup has a depth of flavor and see my tips for making the croutons that go under the cheese when serving.
Recipe Ingredients
- Onions – Use sweet yellow onions (white or yellow, or red onions work too)
- Sugar – Optional, only use if you can’t find sweet yellow onions
- Salted Butter – Used to caramelize the onions
- Flour – Added to the butter and onions. This will add some body to the soup.
- Beef broth – Can use chicken if desired.
- Balsamic Vinegar – Adds flavor and touch of tang.
- Worcestershire sauce – My secret ingredient.
- Seasonings – Salt, pepper, oregano, thyme, garlic, and a bay leaf.
- Toppings – Homemade Croutons (recipe below), swiss cheese, and parmesan cheese.
How to carmelize the onions:
- Set a pan to medium-high heat. Add the butter. When the butter is melted, add the onions and sprinkle with salt and pepper.
- Cook the sliced onions until browned and caramelized; this can take 10 or more minutes. Stir often.
- I add the flour to the butter and onions and cook for 2 more minutes.
- Add remaining ingredients.
- Stir.
How long do I cook?
- Place the lid on the slow cooker.
- Cook on HIGH for 4 hours or on low for 8 hours.
How to make 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.
What Can I Use If I Don’t Have 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 – This buttery onion soup is amazing topped with a bit of stuffing mix under the cheese.
How to serve this recipe:
- Fill an oven safe bowl with the French Onion Soup broth. Place the bowl in a pie tin or on a baking sheet. (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 swiss cheese pieces (can use provolone or gruyere) and sprinkle on parmesan cheese.
- Broil until the cheese is golden brown and is bubbly.
What is the best cheese for this recipe?
- Swiss Cheese or Baby Swiss
- Gruyere Cheese
- Mozzarella Cheese
- Parmesan cheese – in addition to the above cheeses.
Can I freeze this soup?
- Yes, you can freeze the leftover soup (without the croutons and cheese).
- Place the cooled soup into freezer ziplock bags or freezer containtes.
- Freezer for up to 3 months.
- Thaw in fridge for 24 hours before needing.
- Reheat on the stove-top or microwave.
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Slow Cooker French Onion Soup Recipe
Rich and decadent French Onion Soup made in a slow cooker. Top with homemade croutons and cheese, then broil.
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Servings: 10
Calories: 132kcal
Equipment Needed:
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.
How to Video:
Recipe Notes:
What can I use instead of bread for topping this soup?
- 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 – Cut a loaf of store-bought garlic bread into cubes. Broil until crisp and browned.
- Stove-top stuffing – This buttery onion soup is amazing topped with a bit of stuffing mix under the cheese.
- Yes, you can freeze the leftover soup (without the croutons and cheese).
- Place the cooled soup into freezer ziplock bags or freezer containers.
- Freezer for up to 3 months.
- Thaw in fridge for 24 hours before needing.
- Reheat on the stove-top or microwave.
- Swiss Cheese or Baby Swiss
- Gruyere Cheese
- Mozzarella Cheese
- Parmesan cheese – in addition to the above cheeses.
Nutrition Information:
Calories: 132kcal | Carbohydrates: 9g | Protein: 3g | Fat: 10g | Saturated Fat: 6g | Cholesterol: 24mg | Sodium: 954mg | Potassium: 186mg | Fiber: 1g | Sugar: 3g | Vitamin A: 282IU | Vitamin C: 4mg | Calcium: 28mg | Iron: 1mg
Nutrition info is auto-generated. This information is an estimate; if you are on a special diet, please use your own calculations.
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Amazing flavours! Thank you for this recipe.
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 . .
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.
Great soup! Thanks for the recipe!
Can I use Vegetable Broth
yes