# What You'll Need:
→ Alliums
01 - 4 large yellow onions, thinly sliced
02 - 2 large leeks, white and light green parts only, cleaned and thinly sliced
03 - 3 shallots, thinly sliced
04 - 3 garlic cloves, minced
→ Fats
05 - 3 tablespoons unsalted butter
06 - 2 tablespoons olive oil
→ Broth & Umami
07 - 8 cups high-quality beef broth
08 - 1 tablespoon Worcestershire sauce
09 - 2 teaspoons soy sauce
10 - 1/2 cup dry white wine
11 - 2 teaspoons fresh thyme leaves or 1 teaspoon dried thyme
12 - 1 bay leaf
→ Bread & Cheese
13 - 1 baguette, sliced into 1/2-inch rounds
14 - 2 cups Gruyère cheese, grated
15 - 1/2 cup Parmesan cheese, grated
→ Seasonings
16 - Salt and freshly ground black pepper to taste
# Method:
01 - In a large heavy-bottomed pot or Dutch oven, heat the butter and olive oil over medium heat until the butter is melted and foaming.
02 - Add the sliced onions, leeks, and shallots. Sauté while stirring frequently until very soft and deep golden brown, approximately 35 to 40 minutes. Add minced garlic and cook for 2 additional minutes.
03 - Pour in the dry white wine and scrape the bottom of the pot with a wooden spoon to release all browned bits and concentrated flavors.
04 - Stir in the beef broth, Worcestershire sauce, soy sauce, thyme, and bay leaf. Bring the mixture to a simmer over medium-high heat.
05 - Reduce heat to low and cook uncovered for 30 minutes, stirring occasionally to ensure even flavor distribution. Remove and discard the bay leaf.
06 - Taste the soup and adjust seasoning with salt and freshly ground black pepper as needed.
07 - Preheat the oven broiler to high. Arrange baguette slices on a baking sheet in a single layer. Toast under the broiler until golden on both sides, approximately 1 to 2 minutes per side. Monitor closely to prevent burning.
08 - Ladle the hot soup into oven-safe bowls. Top each bowl with toasted baguette slices and distribute a generous amount of grated Gruyère cheese over the bread.
09 - Place the filled bowls under the broiler until the cheese is fully melted and bubbly with light browning on top, approximately 3 to 5 minutes.
10 - Remove bowls from the broiler using oven mitts and serve immediately. Garnish with additional fresh thyme if desired.