Step-by-Step Method

Step 1: Prepare the Onions

  1. Slice the Onions:

    • Peel the onions and slice them thinly into even rings for consistent caramelization.

  2. Heat Butter and Oil:

    • In a large, heavy-bottomed pot or Dutch oven, heat the butter and olive oil over medium heat until the butter melts.

  3. Caramelize the Onions:

    • Add the sliced onions to the pot and stir to coat them evenly in the butter and oil.
    • Sprinkle with sugar (to help with caramelization) and a pinch of salt.
    • Cook the onions, stirring occasionally, for 25-35 minutes or until they are golden brown and deeply caramelized. Reduce the heat if they start to burn.

Step 2: Build the Soup Base

  1. Deglaze the Pot:

    • Pour in the white wine or dry sherry to deglaze the pot, scraping up any browned bits from the bottom. This adds depth of flavor.

  2. Add Broth and Herbs:

    • Stir in the beef broth, thyme sprigs, and bay leaf. Bring the mixture to a gentle boil, then reduce the heat to low and let it simmer for 20-30 minutes.

  3. Season to Taste:

    • Remove the thyme sprigs and bay leaf. Taste the soup and adjust the seasoning with salt and freshly ground black pepper.

Step 3: Prepare the Topping

  1. Toast the Baguette Slices:
    • Preheat your oven to 375°F (190°C).
    • Place the baguette slices on a baking sheet and toast them for 5-7 minutes on each side until crisp.
  2. Grate the Cheese:
    • While the bread is toasting, grate the Gruyère cheese and set it aside.

Step 4: Assemble and Broil

  1. Ladle the Soup:

    • Divide the hot soup among oven-safe bowls or crocks, leaving space at the top for the bread and cheese.

  2. Add the Topping:

    • Place a toasted baguette slice on top of each bowl of soup. Sprinkle generously with grated Gruyère cheese.

  3. Broil Until Golden:

    • Place the bowls on a baking sheet and transfer them to the oven under the broiler.
    • Broil for 2-4 minutes, or until the cheese is melted, bubbly, and golden brown. Keep a close eye to prevent burning.

Serving Suggestions

  • Serve the soup hot, garnished with a sprig of fresh thyme or a dusting of nutmeg for added aroma.
  • Pair with a crisp green salad or a glass of dry white wine for a complete, elegant meal.