Last Updated on October 12, 2026 by Carrie Korem, FNTP
French Onion Soup in the Slow Cooker is made with onions, butter, broth, herbs and spices and is perfect for a fall meal! After you make the soup in the slow cooker, you top it with toasted sourdough with Swiss cheese. It’s so easy and flavorful!
Ingredients for Slow Cooker French Onion Soup
- Unsalted butter
- Celtic sea salt
- Yellow onions
- Garlic cloves
- Thyme
- Meat stock or bone broth
- Rind of parmesan (optional)
- Sherry vinegar
- Worcestershire sauce
- Sourdough or gf bread
- Swiss or gruyere cheese
How to Make French Onion Soup in the Slow Cooker
Turn the slow cooker to the hottest setting. Place the butter in the bowl of the slow cooker and let the butter melt.
Meanwhile, peel and slice the onions. When the butter is melted, add the onions, sea salt, garlic and thyme to the butter and toss to combine. Put the lid on the slow cooker and cook for 6 hours, stirring once half-way through (at the 3 hour mark).Â
After 6 hours, add the broth, parmesan rind (if using), vinegar, and Worcestershire. Stir to combine. Put the lid back on and cook for 1 hour.Â
About 20 minutes before serving. Preheat the oven to 375ºF. Place the sourdough on a baking sheet and top with the Swiss cheese. Bake in the oven for about 10 minutes until the cheese is melted.Â
When you’re ready to serve the soup, ladle a portion of soup into a bowl and then top with your toasted bread and cheese.Â
Do you have to cook onions before putting in the slow cooker
No. This recipe is completely made in the slow cooker! The key is to cook the onions first, and then about an hour before serving, you add the broth, herbs and seasonings.
What is the best non-toxic slow cooker
Many slow cookers contain non-stick coatings or lead or aluminum into the food, so it’s important to choose a slow cooker that is non-toxic. I personally use this slow cooker (the code ORGANIC10 saves 10%). It’s ceramic and non-toxic. And, the insert comes out easily for cleaning.
More slow-cooker recipes to enjoy:
Slow-Cooker Red Beans and RiceÂ
6-Ingredient Slow Cooker Pot Roast
Slow Cooker Pepper Steak
French Onion Soup in the Slow Cooker
- Prep Time: 15
- Cook Time: 7 hours
- Total Time: 7 hours 15 minutes
- Yield: Serves 4
- Category: Dinner
- Method: Slow Cooking
Ingredients
- 5 tablespoons unsalted butter, grated or cut into very small pieces
- 1 1/2 tablespoons Celtic sea salt
- 8 cups sliced onion, about 4 medium onions
- 4 cloves garlic
- 2 teaspoons dried thyme
- 5 cups meat stock or bone broth
- 1 rind of parmesan (optional)
- 1 tablespoons sherry vinegar
- 1 teaspoon Worcestershire sauce
- 4 slices of sourdough or gf bread
- 4 thick slices swiss or gruyere cheese
Instructions
- Turn the slow cooker to the hottest setting. Place the butter in the bowl of the slow cooker and let the butter melt.
- Meanwhile, peel and slice the onions. When the butter is melted, add the onions, sea salt, garlic and thyme to the butter and toss to combine. Put the lid on the slow cooker and cook for 6 hours, stirring once half-way through (at the 3 hour mark).
- After 6 hours, add the broth, parmesan rind (if using), vinegar, and Worcestershire. Stir to combine. Put the lid back on and cook for 1 hour.
- About 20 minutes before serving. Preheat the oven to 375ºF. Place the sourdough on a baking sheet and top with the Swiss cheese. Bake in the oven for about 10 minutes until the cheese is melted.
- When you’re ready to serve the soup, ladle a portion of soup into a bowl and then top with your toasted bread and cheese.
Oh boy… I need to add this to my soup list! 🤩 Question… Can I use coconut amino instead of the Worcestershire sauce which I believe has wheat in it?