Ingredients:

  • tablespoons unsalted butter
  • large yellow onions (about 3 lbs total), thinly and uniformly sliced
  • teaspoon Kosher salt, plus more to taste
  • teaspoon granulated sugar (optional)
  • tablespoons all-purpose flour
  • /2 cup dry sherry or dry white wine
  • cups high-quality beef broth or stock
  • sprigs fresh thyme
  • large bay leaf
  • Freshly ground black pepper to taste
  • loaf baguette, sliced thickly (about 1 inch)
  • tablespoon olive oil or melted butter
  • ounces (2 cups grated) Gruyère cheese, freshly grated

Instructions:

  1. Melt butter in a large, heavy-bottomed Dutch oven over medium heat. Add sliced onions, salt, and sugar. Cook, stirring occasionally, for 20 minutes until softened. Reduce heat to low-medium and continue cooking, stirring every 5–10 minutes, for another 40–55 minutes until the onions are deep mahogany brown.
  2. Stir in the flour and cook for 2 minutes until lightly toasted.
  3. Pour in the sherry or wine. Scrape up any browned bits (the fond) stuck to the bottom of the pot. Cook until the liquid is nearly evaporated, about 3 minutes.
  4. Pour in the beef broth. Add thyme sprigs and bay leaf. Bring to a gentle simmer, then cover partially and cook for 30 minutes to allow flavours to meld. Adjust seasoning with pepper and salt if necessary. Remove and discard the thyme sprigs and bay leaf.
  5. Preheat oven/broiler. Lightly brush baguette slices with olive oil or melted butter. Toast on a baking sheet until lightly golden brown (approx. 5 minutes).
  6. Ladle the hot soup into 4 oven-safe crocks, filling them about 3/4 full. Place one or two toasted baguette slices on top of the soup. Generously mound grated Gruyère over the bread, ensuring the cheese slightly overlaps the rim.
  7. Place the bowls carefully on a baking sheet. Broil on a high rack for 2–4 minutes, watching constantly, until the cheese is bubbly, melted, and beautifully browned for the classic gratinée finish.