Description
A rich and comforting Slow Cooker French Onion Soup recipe that slowly caramelizes onions to develop deep flavors. This easy recipe uses a slow cooker to cook the onions to perfect golden brown sweetness, enhanced with garlic, balsamic vinegar, and sherry. Topped with toasted baguette slices and melted Gruyère cheese under the broiler, this classic French soup is perfect for a cozy meal with minimal hands-on effort.
Ingredients
Soup Ingredients
- 4 yellow onions (thinly sliced)
- 2 tablespoons butter (or olive oil for a vegan option)
- 1 tablespoon sugar
- 4 cloves garlic (minced)
- 1 tablespoon balsamic vinegar
- 2 tablespoons dry sherry (optional)
- 8 cups vegetable broth (low-sodium)
- 2 sprigs fresh thyme (or 1 teaspoon dried thyme)
- 2 bay leaves
- ½ teaspoon salt
- ¼ teaspoon black pepper (adjust to taste)
- 1 tablespoon soy sauce (or tamari for gluten-free)
Toppings
- 1 baguette (sliced)
- 2 cups Gruyère cheese (freshly shredded)
Instructions
- Caramelize the Onions: Set your slow cooker to high. Add melted butter (or olive oil), sliced onions, and sugar. Stir to coat the onions evenly. Prop the lid open slightly to allow steam to escape and cook for 6-8 hours on low, stirring occasionally, until onions are golden brown and soft.
- Add Garlic: Once onions are caramelized, add minced garlic and cook for another 2-3 minutes on low, stirring occasionally to release the garlic aroma.
- Deglaze the Cooker: Add balsamic vinegar and sherry to deglaze the slow cooker. Stir well to lift any browned bits off the bottom for extra flavor.
- Add Broth and Seasonings: Pour in vegetable broth, add thyme sprigs, bay leaves, soy sauce, salt, and black pepper. Stir to combine, cover, and cook on low for an additional 4-6 hours to develop rich soup flavors.
- Toast the Baguette: Preheat oven to 400°F (200°C). Arrange baguette slices on a baking sheet and toast the slices until golden and crispy, about 5-7 minutes.
- Prepare Soup Bowls: Remove thyme sprigs and bay leaves from the soup. Ladle the soup into oven-safe bowls, place toasted baguette slices on top, and generously sprinkle with shredded Gruyère cheese.
- Broil It: Place the bowls under the oven broiler for a few minutes until the cheese melts and becomes bubbly and golden brown.
- Serve Warm: Serve immediately with optional extra thyme garnish or a drizzle of balsamic reduction for an added touch of sweetness and acidity.
Notes
- For a vegan version, use olive oil instead of butter and a dairy-free cheese substitute.
- Dry sherry is optional but adds depth; you can substitute with white wine or omit for a non-alcoholic version.
- Use gluten-free bread and tamari soy sauce to make the recipe gluten-free.
- If you do not have a slow cooker, caramelize onions on the stovetop over low heat, stirring frequently to prevent burning.
- Adjust seasoning to taste, especially salt, depending on the broth’s sodium content.
- Broil the soup carefully as cheese can burn quickly under high heat.
