French Onion Soup Recipe

Prepare onions

Peel and halve the onions, then thinly slice into half-moons so you have about 6 cups. Using a sharp knife yields even slices that cook evenly.

Caramelize onions

In a large heavy-bottomed pot or Dutch oven, heat the butter and 1 tablespoon olive oil over medium heat until the butter foams. Add the sliced onions, sprinkle with 1 teaspoon salt and 1 teaspoon sugar, and stir to coat. Cook, stirring every 3–5 minutes, for 25–35 minutes until onions are deeply golden-brown and caramelized. If onions begin to stick or brown too quickly, lower the heat. Reduce heat as needed to maintain a gentle brown without burning.

Add flour

Push the caramelized onions to the side or make a well in the center. Sprinkle 1 tablespoon of all-purpose flour over the onions and cook, stirring constantly, for 1–2 minutes to remove the raw flour taste and to help thicken the broth slightly.

Deglaze

Pour in 1 cup dry white wine to deglaze the pot, scraping up any browned bits on the bottom with a wooden spoon. Simmer for 2–3 minutes until the wine reduces by about half.

Simmer soup

Add 6 cups beef stock, 1 bay leaf, 2 tablespoons fresh thyme (or 2 sprigs tied), and 1 teaspoon Worcestershire sauce. Bring the mixture to a gentle simmer, reduce heat to low, and cook uncovered for 20–25 minutes to meld flavors. Taste and adjust seasoning with additional salt and pepper if necessary. Remove and discard the bay leaf and thyme stems if used.

Prepare croutons

While the soup simmers, preheat the oven to 400°F (200°C). Arrange 10 baguette slices on a baking sheet, brush lightly with 1 tablespoon olive oil, and toast in the oven for 6–8 minutes until lightly golden. Rub the warm toasts with the cut side of 1 garlic clove for a subtle garlic flavor.

Assemble and broil

Ladle the hot soup into ovenproof bowls or crocks, leaving about 1/2 inch headroom. Place one or two toasted baguette slices on top of each bowl of soup (they can float). Generously sprinkle about 1/4 to 1/3 cup grated Gruyère over each bowl, finishing with a light dusting of the 1 tablespoon grated Parmesan for extra flavor. Place the bowls on a baking sheet and broil on high 4–6 inches from the broiler for 2–4 minutes until the cheese is bubbling and golden-brown. Watch carefully to avoid burning.

Finish and serve

Carefully remove the hot bowls from the oven (use oven mitts). Let sit 1–2 minutes to stabilize, then serve immediately. Optionally garnish with a small sprig of fresh thyme or cracked black pepper to taste.