Step by step

Method

4 steps

1. 1

   Melt 3 tablespoons unsalted butter with 1 tablespoon olive oil in a large Dutch oven over medium heat. Add 4 large thinly sliced yellow onions and 1 teaspoon kosher salt. Cook, stirring often, 30–35 minutes until the onions are very soft and golden — don't rush; pale onions make pale soup.

2. 2

   Stir in 1 teaspoon sugar and cook 3–5 minutes more until the onions are deeply caramelized and jammy. Add 3 minced garlic cloves and cook 30 seconds until fragrant.

3. 3

   Sprinkle in 1 tablespoon all-purpose flour and stir 1 full minute until it smells toasty. Gradually pour in 6 cups low-sodium beef broth, scraping up the browned bits. Add 4 fresh thyme sprigs and 1 bay leaf. Simmer uncovered 20 minutes. Season with black pepper; fish out the thyme and bay leaf.

4. 4

   Heat the broiler. Ladle the soup into broiler-safe bowls on a sheet pan. Top each with baguette slices (about 8 total) and a generous pile of shredded Gruyère (about 1½ cups total). Broil 2–4 minutes until the cheese is bubbling and browned in spots. Serve carefully — the bowls are ripping hot. You want deeply caramelized French onion soup under stretchy Gruyère toast — not sweet undercooked onions or a thin salty broth with rubbery cheese.