Ingredients:

  • 3 pounds yellow onions, thinly sliced (1.4 kg)
  • 4 tablespoons unsalted butter (56 g)
  • 2 tablespoons olive oil (30 ml)
  • 1 teaspoon granulated sugar (5 g)
  • 1/2 teaspoon baking soda (2.5 ml/g)
  • 1/4 cup dry sherry (60 ml)
  • 8 cups beef broth (2 liters)
  • 4 cups water (1 liter)
  • 2 bay leaves
  • 4 sprigs fresh thyme
  • Salt and freshly ground black pepper to taste
  • 6 baguette slices, approximately 1 inch thick
  • 2 tablespoons olive oil (30 ml)
  • 6 ounces Gruyère cheese, shredded (170 g)
  • Fresh parsley, chopped for garnish (Optional)

Instructions:

  1. Melt butter and olive oil in the pot over medium heat. Add onions, sugar, and baking soda. Cook, stirring frequently, until the onions are deeply golden brown and caramelized (about 1-1.5 hours).
  2. Add sherry to the pot and scrape up any browned bits from the bottom. Cook until the sherry has almost evaporated.
  3. Pour in beef broth and water. Add bay leaves and thyme sprigs. Bring to a simmer, then reduce heat and simmer for at least 30 minutes to allow the flavors to meld.
  4. Preheat oven to 400°F (200°C). Brush baguette slices with olive oil and bake on a baking sheet until golden brown and lightly crisp.
  5. Remove bay leaves and thyme sprigs from the soup. Season with salt and pepper to taste. Ladle soup into oven-safe bowls. Top each bowl with a crouton and a generous amount of Gruyère cheese. Broil until the cheese is melted, bubbly, and lightly browned.
  6. Garnish with fresh parsley (if desired) and serve immediately.