Slow Cooker French Onion Soup
This Slow Cooker French Onion Soup is rich, savory, and packed with deep caramelized onion flavor. Sweet golden onions simmer all day in a flavorful beef broth, then get topped with toasted bread and gooey melted cheese. It’s the ultimate cozy comfort food that tastes like it came from a French bistro!
Servings: 8
Calories: 379kcal
Equipment
- Heavy-bottomed pot large
- Wooden spoon
- Slow cooker crockpot
- Ceramic ramekins or oven-safe soup bowls (crocks)
Ingredients
- 6 tbsp butter
- 4 yellow onions large, sliced into rings
- 1 tbsp white sugar
- 2 cloves garlic minced
- ½ cup cooking sherry
- 7 cups reduced-sodium beef broth
- 1 tsp sea salt or to taste
- ¼ tsp dried thyme
- 1 bay leaf
- 8 slices French bread
- ½ cup Gruyere cheese shredded
- ⅓ cup Emmental cheese shredded
- ¼ cup Parmesan cheese freshly shredded
- 2 tbsp mozzarella cheese shredded
Instructions
- Melt the butter in a large pot over medium-high heat. Add the onions and cook for about 10 minutes, stirring occasionally, until softened and translucent. Sprinkle with sugar, reduce heat to medium, and continue cooking, stirring frequently, until deeply caramelized, about 30 minutes. Stir in the garlic and cook for 1 minute.
- Pour in the sherry and scrape up any browned bits from the bottom of the pot to boost flavor.
- Transfer the onion mixture to the slow cooker. Add the beef broth, salt, thyme, and bay leaf. Stir well, cover, and cook on Low for 8 to 10 hours or High for 4 to 6 hours.
- When ready to serve, preheat the oven broiler and position the rack about 8 inches from the heat source.
- Arrange the French bread slices on a baking sheet and broil for 1 to 2 minutes per side, until toasted.
- In a mixing bowl, combine the Gruyere, Emmental, Parmesan, and mozzarella cheeses.
- Ladle the hot soup into oven-safe bowls, filling each about three-quarters full. Place one slice of toasted bread on top of each bowl and sprinkle with about 2 tablespoons of the cheese mixture.
- Place the bowls on a baking sheet and broil for about 2 minutes, or until the cheese is melted, bubbly, and lightly golden. Serve immediately.
Notes
- Caramelizing the onions on the stovetop creates the richest flavor. While you can skip this step and cook everything in the slow cooker, the extra time on the stove makes a big difference.
- For a fun serving idea, set out the soup, toasted bread, and cheese separately and let everyone build their own bowl.
Nutrition
Calories: 379kcal | Carbohydrates: 41g | Protein: 17g | Fat: 16g | Saturated Fat: 9g | Polyunsaturated Fat: 1g | Monounsaturated Fat: 4g | Trans Fat: 0.3g | Cholesterol: 41mg | Sodium: 1272mg | Potassium: 607mg | Fiber: 2g | Sugar: 7g | Vitamin A: 430IU | Vitamin C: 4mg | Calcium: 231mg | Iron: 3mg