The Magical Slow Cooker » Recipes » Soups » Slow Cooker French Onion Soup
by Sarah Olson on | Updated 20 Comments
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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 slow cooker baked potato soup and slow cooker ham and bean soup. If you want a chicken version of this soup, try my Slow Cooker French Onion Chicken recipe.
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.
If you love this soup, then try my Slow Cooker French Onion Dip, or my Slow Cooker French Onion Pot Roast.
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
4.93 from 55 votes
Rich and decadent French Onion Soup made in a slow cooker. Top with homemade croutons and cheese, then broil.
Print Pin Rate
Course: Soup
Cuisine: American
Prep Time: 25 minutes minutes
Cook Time: 4 hours hours
Total Time: 4 hours hours 20 minutes minutes
Servings: 10
Calories: 132kcal
Author: Sarah Olson
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:
Sarah’s 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.
Can I freeze the leftover soup?
- 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.
Best cheeses for this recipe:
- Swiss Cheese or Baby Swiss
- Gruyere Cheese
- Mozzarella Cheese
- Parmesan cheese – in addition to the above cheeses.
Nutritional values do not include croutons or cheese (every bowl size will need different amounts of cheese and croutons, that is why I can not add this value).
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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Try one of these soups next:
- Slow Cooker Stuffed Pepper Soup
- Slow Cooker Broccoli Cheese Soup
- Slow Cooker Corned Beef and Cabbage Soup
- Slow Cooker Turkey Chowder
- Slow Cooker Tomato Soup
- Slow Cooker Black Bean Soup
- Slow Cooker Chicken Noodle Soup
