Slow cooker French onion soup is a warm bowl of fall comfort food. This Crock Pot recipe turns a classic into a mostly hands-off, gourmet meal perfect for an easy dinner.
Sweet onions are simmered in beef broth for hours and topped off with delicious cheesy bread. This rich and satisfying soup is perfect for busy days or cozy weekends.
My favorite thing about this recipe is how easy it is to caramelize the onions in the slow cooker. Traditionally, to caramelize onions for French onion soup, you must stir them frequently for about an hour. An hour in the kitchen stirring onions is not my idea of a good time!
You still have to stir the onions for this slow cooker soup recipe, but just once every hour. That is the kind of low-commitment effort I can handle. And I still get to cozy up with a bowl of warm and irresistible soup.
Keep reading for the step-by-step directions on how to make this soup, along with some crispy, cheesy bread to top it off.
The slow cooker is perfect for making soups! Try Olive Garden gnocchi soup, Mexican street corn soup, or ham and potato soup for more delicious recipe ideas.
🥘Ingredient Notes
For exact amounts needed see the recipe card below
- Onions: Onions are the star of this recipe. I love using large, sweet onions, like candy onions or Vidalias, for this soup. They caramelize beautifully and give the soup that irresistible sweetness. But really, any variety of sweet onions will do the trick.
- Butter
- Flour
- Broth: If you’re vegetarian or vegan, use veggie or mushroom stock.
- Worcestershire sauce
- Thyme
- Bread and cheese: One of the best parts of French onion soup is the cheesy bread on top! I like to use French or Italian bread topped with shredded Gruyere cheese.
🥣How to Make Slow Cooker French Onion Soup
- Slice your onions and toss them with flour in the crock of your slow cooker.
- Add pats of butter over the onions, season with salt and pepper, and let the slow cooker work its magic on high for 5-6 hours. Stir the onions every hour or so to prevent burning and ensure even caramelization.
- Once the onions are a deep, caramelized brown, add Worcestershire sauce, thyme, beef broth, and water. Stir and let the soup cook for another 1-2 hours until heated.
- While the soup is finishing, make your cheesy toasts in the air fryer or the oven.
- Oven baked: Preheat your oven to 350 degrees F and arrange bread slices on a parchment-lined baking sheet. Pile some shredded Gruyere on each slice, and bake for 8-10 minutes until the cheese melts and bubbles.
- Air fried: Arrange the bread slices in the air fryer basket. Pile the Gruyere on each slice and bake at 350 degrees F for 5 minutes until the cheese melts and bubbles.
🍴Serving Ideas
Ladle the hot soup into bowls, top each with a cheesy toast, garnish with fresh parsley, and enjoy! If you want to try something different, here are some ideas:
- Bread bowl: Hollow out a crusty round loaf of bread, ladle in the hot soup, and top with shredded cheese.
- Grilled cheese dippers: Instead of putting the cheesy toast on top of the soup, serve it on the side as grilled cheese dippers.
- French onion soup au gratin: Pour the hot soup into oven-safe bowls, top with a slice of bread and plenty of shredded cheese, and broil until the cheese melts.
💭How to Store
This soup keeps well in the fridge, so it’s perfect for meal prep or making ahead for busy weeknights. The soup will keep for 2-3 days in an airtight container in the fridge.
You can store the cheesy toasts separately or make fresh ones when you’re ready to serve. Reheat the soup in the microwave or a saucepan on the stove.
I don’t recommend freezing this recipe. The texture of the onions can become mushy, and the broth can separate when thawed. It’s best to enjoy this soup fresh or store it in the fridge for a few days.
⭐Tips
Be sure to check out the step by step instructions
- While you can certainly use just one type of onion, you can also use a mix of sweet onions for extra flavor.
- This recipe is not a “set it and forget it” slow cooker recipe, as you do need to be present to stir the onions as they caramelize throughout the day. However, if you prefer, you can caramelize the onions in a skillet first: Melt the butter over medium-high heat and add the sliced onions. Cook for 45-60 minutes, stirring often and sprinkling with salt as they cook, until they caramelize. Add them to the crockpot along with the remaining ingredients and cook on low for 6 hours or on high for 3 hours.
- To make this soup vegetarian, swap the beef broth for vegetable broth and use vegetarian-friendly cheese on top (or skip the cheese altogether). You will also need to skip the Worcestershire sauce.
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Slow Cooker French Onion Soup Recipe
Ingredients
- 4-5 large sweet onions sliced
- 4 tablespoons butter sliced into pats
- 2 tablespoons flour
- ½ teaspoon salt
- ¼ teaspoon ground black pepper
- 1 tablespoon Worcestershire sauce optional, leave out for a vegetarian recipe
- ½ teaspoon ground thyme
- 8 cups broth
- 4 cups water
- 2 tablespoons chopped fresh parsley divided
- French or Italian bread sliced into eight slices
- 4 ounces Gruyere cheese shredded
Instructions
- Place the onions and flour in the crock of your slow cooker. Use tongs to toss so that the onions are well-coated in the four.4-5 large sweet onions, 2 tablespoons flour
- Add the butter pats over the coated onions, then season with salt & pepper.4 tablespoons butter, ½ teaspoon salt, ¼ teaspoon ground black pepper
- Place the lid on your slow cooker and let the onions cook on high for 5-6 hours. Stir once every hour to ensure the butter is distributed and the onions are caramelizing and not burning.
- When the onions have reached a deep brown, caramelized color, add the Worcestershire sauce and thyme.1 tablespoon Worcestershire sauce, ½ teaspoon ground thyme
- Add the beef broth and water and stir to combine.8 cups broth, 4 cups water
- Continue cooking for another 1-2 hours or until the flavors come together and the soup is heated. Serve in bowls and garnish with fresh parsley.2 tablespoons chopped fresh parsley
- As described below, make the cheesy toast in either the oven or the air fryer.
- Garnish the cheese toasts with additional parsley.
- Place one slice of cheese toast in your French onion soup bowl and serve hot.
To make cheese toasts in the oven:
- Preheat your oven to 350 degrees F.
- Line a baking sheet with parchment paper and arrange the bread slices.French or Italian bread
- Place a small pile of Gruyere cheese in the center of each slice of bread.4 ounces Gruyere cheese
- Bake in the oven for 8-10 minutes or until the cheese is melted and just starting to crisp & brown on the edges.
To make cheese toasts in the air fryer:
- Arrange the bread slices in the air fryer basket.
- Place a small pile of Gruyere cheese in the center of each slice of bread.
- Bake in the air fryer at 350 degrees F for 5 minutes or until the cheese is melted and just starting to crisp & brown on the edges.
Notes
- This is not a “set it and forget it” type of slow cooker recipe, as you do need to be present to stir the onions as they caramelize throughout the day. However, if you prefer, you can caramelize the onions in a skillet first: Melt the butter over medium-high heat and add the sliced onions. Cook for 45-60 minutes, stirring often and sprinkling with salt as they cook, until they caramelize. Add them to the crockpot along with the remaining ingredients and cook on low for 8 hours or on high for 4 hours.
- While you can certainly use just one type of onion, you can also use a mix of sweet onions for extra flavor.
- Beef broth is traditional, but vegetable or mushroom broth works well too.
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Nutrition Information
Nutrition facts are estimates.
Made it as directed. Not much flavor in this soup! Would recommend less water and more seasoning to any who try!