French Onion Soup Recipe

Prepare onions

Peel and trim 6 large yellow onions. Cut in half pole-to-pole and slice thinly (about 1/8 to 1/4 inch). You should have roughly 6 cups thin slices.

Caramelize onions

In a large heavy-bottomed pot or Dutch oven, heat 3 tablespoons unsalted butter and 1 tablespoon olive oil over medium heat until butter foams. Add sliced onions, 1 teaspoon coarse salt and 1 teaspoon granulated sugar. Toss to coat. Cook, stirring frequently, for 30–40 minutes, reducing heat to medium-low as needed to prevent burning. Scrape browned bits from the bottom occasionally. The onions should become deep golden brown and sweet. If they brown too fast, lower the heat.

Deglaze

Increase heat to medium-high, add 1 cup dry white wine (or omit and use a splash of stock) to deglaze the pot. Use a wooden spoon to scrape up all browned fond from the bottom. Let the wine reduce by half, about 2–3 minutes.

Simmer soup

Add 6 cups beef stock, 2 bay leaves, about 1 tablespoon fresh thyme stems (or 1 teaspoon dried thyme), and 1 teaspoon Worcestershire sauce. Bring to a simmer, then reduce heat to low and simmer gently, uncovered, for 20–30 minutes to let flavors meld. Taste and adjust seasoning with additional salt and pepper as needed. Remove bay leaves and thyme stems before serving.

Prepare bread

While the soup simmers, preheat the oven to 400°F (200°C). Slice the baguette into 1/2-inch thick slices. Lightly brush both sides with 1 tablespoon olive oil. Optional: rub the toasted slices with a cut garlic clove for extra flavor.

Toast bread

Arrange the slices on a baking sheet and toast in the oven for 6–8 minutes, flipping once, until lightly golden and crisp. Remove from oven and set aside.

Prep cheese

Grate 2 cups Gruyère and 1 tablespoon Parmesan. Mix together and have ready to top the toasts and soup.

Assemble croûtes

Ladle hot soup into oven-safe bowls or crocks, filling them about 3/4 full. Place a toasted baguette slice on top of each bowl (or float two smaller slices). Generously heap grated Gruyère on each slice, finishing with a sprinkle of Parmesan.

Broil

Place the bowls on a baking sheet and slide under a hot broiler set to high, about 6 inches from the heat source. Broil for 2–4 minutes until cheese is melted, bubbly and lightly browned. Watch carefully to avoid burning. Alternatively, bake at 450°F (230°C) until cheese melts, about 5–8 minutes.

Remove bowls from oven with oven mitts. Sprinkle each with a pinch (about 1/8–1/4 tsp) of finishing flaky salt and a little chopped parsley or extra thyme if using. Let cool 2–3 minutes before serving — the cheese and soup will be very hot.