Ingredients:

  • 4 large onions, thinly sliced (about 1 kg)
  • 4 tablespoons unsalted butter (57 g)
  • 1 tablespoon olive oil (15 ml)
  • 1 teaspoon salt (5 g)
  • 1 teaspoon sugar (5 g)
  • 4 cups beef broth (960 ml)
  • 1 cup white wine (240 ml) (such as Sauvignon Blanc)
  • 1 tablespoon fresh thyme, chopped (or 1 teaspoon dried thyme) (15 g)
  • 1 bay leaf
  • Freshly ground black pepper, to taste
  • 4 slices of baguette or sourdough, toasted
  • 1 ½ cups Gruyère cheese, grated (150 g)
  • ½ cup Parmesan cheese, grated (50 g)

Instructions:

  1. Heat the butter and olive oil in the pot over medium heat. Add sliced onions and salt; stir to coat. Cook, stirring occasionally, for about 30-40 minutes until the onions are deeply caramelized and golden brown. Add sugar halfway through to enhance caramelization.
  2. Pour in the white wine, scraping the bottom of the pot to release any browned bits. Allow it to simmer until reduced by half.
  3. Pour in the beef broth and add thyme, bay leaf, and black pepper. Bring to a simmer and cook for an additional 15-20 minutes.
  4. While the soup simmers, preheat the oven to 350°F (175°C). Toast the bread slices in the oven until golden brown.
  5. Remove the bay leaf, and ladle soup into oven-safe bowls. Top each bowl with toasted bread and an even layer of Gruyère and Parmesan cheese. Place bowls under the broiler for a few minutes until the cheese is bubbly and golden.