Slow Cooker French Onion Soup, a comforting classic made with caramelized onions, rich broth, and topped with crusty bread and melted cheese. The slow cooker does most of the work, making this a simple, hands-off way to enjoy a deeply flavorful soup.
Slow Cooker French Onion Soup Recipe
This French Onion Soup is slow-cooked to perfection, allowing the onions to caramelize and the flavors to meld beautifully. It’s topped with toasted bread and gooey melted cheese for a satisfying, hearty meal.
Ingredients
- 6 large yellow onions, thinly sliced
- 3 tablespoons unsalted butter
- 1 tablespoon olive oil
- 1 teaspoon sugar (to help with caramelizing)
- 3 cloves garlic, minced
- 1 tablespoon all-purpose flour (optional, for thickening)
- 8 cups beef broth (or vegetable broth for a lighter option)
- 1/2 cup dry white wine or sherry
- 2 bay leaves
- 1 teaspoon fresh thyme (or 1/2 teaspoon dried thyme)
- Salt and pepper to taste
- French baguette, sliced
- 2 cups grated Gruyère cheese (or Swiss cheese)
Instructions
1. Caramelize the Onions
In a large skillet, melt the butter with olive oil over medium heat. Add the sliced onions and sprinkle with the sugar to help them caramelize. Cook the onions for about 15-20 minutes, stirring frequently, until they are golden brown and deeply caramelized.
You can also caramelize the onions directly in your slow cooker by cooking on high for about 1 hour, stirring occasionally, but using a skillet speeds up the process.
2. Transfer to Slow Cooker
Once the onions are caramelized, transfer them to the slow cooker. Add the minced garlic and sprinkle with flour if you prefer a slightly thicker soup. Stir well to combine.
3. Add Broth and Wine
Pour in the beef broth and white wine or sherry. Add the bay leaves, thyme, and season with salt and pepper. Stir to combine all the ingredients.
4. Slow Cook
Cover the slow cooker and cook on low for 6-8 hours or on high for 3-4 hours, until the onions are soft and the flavors are well blended. Remove the bay leaves before serving.
5. Prepare the Bread and Cheese
About 10 minutes before serving, preheat your oven’s broiler. Slice the French baguette into 1-inch thick pieces and place them on a baking sheet. Toast them under the broiler for 2-3 minutes until golden brown. Sprinkle each slice with a generous amount of grated Gruyère cheese and return to the broiler for another 2-3 minutes, until the cheese is bubbly and melted.
6. Serve the Soup
Ladle the soup into bowls and top each with a slice of the toasted bread and melted cheese. For an authentic presentation, you can place the cheese-topped bread directly on the soup and broil the whole bowl until the cheese is bubbly and golden brown.
Serving Suggestions
- Serve this Slow Cooker French Onion Soup with a simple green salad or alongside other French-inspired dishes like quiche or croque monsieur.
- Add a side of extra crusty bread for dipping into the rich broth.
Tips for the Best French Onion Soup
- Caramelize the onions well: The key to a rich, flavorful French onion soup is properly caramelizing the onions. Take your time to get them deep golden brown—this will add sweetness and depth to the soup.
- Use quality broth: A good-quality beef broth makes a big difference in the flavor of this soup. You can also use vegetable or chicken broth if you prefer.
- Gruyère cheese is best: Gruyère is the classic choice for French Onion Soup because it melts beautifully and has a nutty, rich flavor. If you can’t find Gruyère, use Swiss or even mozzarella for a delicious alternative.
Variations
- Vegetarian French Onion Soup: Use vegetable broth instead of beef broth for a lighter, vegetarian-friendly version.
- Add a splash of brandy: For extra richness, you can stir in a tablespoon of brandy or cognac toward the end of cooking.
- Thicken the soup: If you prefer a thicker soup, you can add an extra tablespoon of flour to the caramelized onions or whisk in a slurry of cornstarch and water.
Storage and Reheating
- Store any leftover French Onion Soup in an airtight container in the refrigerator for up to 3 days. Reheat on the stove over low heat or in the microwave.
- To freeze, transfer the soup (without the bread and cheese) to a freezer-safe container and freeze for up to 3 months. Thaw in the refrigerator overnight before reheating.
Enjoy this comforting, flavorful Slow Cooker French Onion Soup, perfect for a cozy evening or special dinner!