Ingredients
1 tablespoon olive oil
3 tablespoons unsalted butter
4 large yellow onions, thinly sliced
1 teaspoon sugar
1 teaspoon salt
1/4 teaspoon freshly ground black pepper
8 cups low-sodium beef broth
1/2 cup water
2 teaspoons fresh thyme leaves (or 1 teaspoon dried thyme)
1 bay leaf
1 baguette, sliced and toasted
2 cups grated Gruyère cheese
Instructions
1. Caramelize the Onions
Heat the Fat: Combine olive oil and butter in a large pot over medium heat. Heat until melted and shimmering.
Cook the Onions: Add sliced onions, sugar, and salt. Stir to coat the onions evenly.
Caramelize: Cook for 30–40 minutes, stirring occasionally, until the onions are soft, golden, and deeply caramelized. Adjust the heat as needed to avoid burning.
2. Build the Soup Base
Add Aromatics: Stir in the thyme, black pepper, and bay leaf. Cook for 1 minute to release their flavors.
Incorporate Liquids: Add beef broth and water. Bring the soup to a boil, then reduce heat to low. Simmer uncovered for 30 minutes to blend the flavors.
Finish the Base: Remove and discard the bay leaf.
3. Prepare the Bread
Toast the Baguette: Preheat the broiler. Arrange baguette slices on a baking sheet and toast for 1–2 minutes per side, until golden brown.
4. Assemble and Broil
Ladle the Soup: Divide the soup into oven-safe bowls.
Top with Bread and Cheese: Place a toasted baguette slice on top of the soup in each bowl. Sprinkle generously with grated Gruyère cheese.
Broil: Place the bowls under the broiler for 2–3 minutes, or until the cheese is melted, bubbly, and golden.
5. Serve and Enjoy
Garnish: Optionally, sprinkle with fresh thyme leaves for extra aroma.
Savor: Serve hot and enjoy this comforting, flavorful classic.