French Onion Soup Recipe

Prepare onions

Peel and thinly slice the yellow onions into half-moons. Aim for consistent slices about 1/8-inch thick so they caramelize evenly.

In a large heavy-bottomed pot or Dutch oven, heat the butter and 1 tablespoon olive oil over medium heat until the butter foams. The oil raises the butter's smoke point and helps prevent burning.

Add the sliced onions, 1 teaspoon granulated sugar, and 1 teaspoon salt. Stir to coat the onions in fat. Spread them into an even layer and cook, stirring frequently, for 30–40 minutes until deep golden brown and sweet. If edges seem to brown too quickly, reduce heat to medium-low. Scrape browned bits from the bottom as needed to prevent burning.

When onions are richly caramelized, stir in the minced garlic and cook 30–60 seconds until fragrant.

Increase heat to medium-high and pour in the 3 tablespoons dry white wine or sherry to deglaze the pot. Use a wooden spoon to scrape up any browned fond from the bottom. Simmer until the wine has mostly evaporated, about 1–2 minutes.

Add the 6 cups beef stock, 1 teaspoon beef bouillon paste if using, the bay leaf, and the thyme sprigs. Bring to a gentle simmer, then reduce heat to low and simmer uncovered for 20–30 minutes to let flavors meld. Taste and adjust seasoning with additional salt and 1/2 teaspoon freshly ground black pepper if needed. Remove and discard thyme stems and bay leaf before serving.

While the soup simmers, preheat the oven to 400°F (200°C). Arrange the baguette slices on a baking sheet. Brush each side lightly with the 1 tablespoon olive oil and toast in the oven for 6–8 minutes, turning once, until crisp and golden. Alternatively, toast under a broiler, watching closely to avoid burning.

Remove toasted bread and, if desired, rub one side of each slice with the halved garlic clove to impart a subtle garlic aroma.

Ladle the hot soup into ovenproof bowls (about 1 to 1 1/2 cups soup per bowl). Place one or two toasted baguette slices on top of each bowl, then divide the grated Gruyère evenly over the bread. Sprinkle a little Parmesan over each if using. Add a crack of freshly ground black pepper to taste.

Place the filled bowls on a baking sheet to catch drips and transfer to the oven (or under a broiler) set to 450°F (230°C) or broil high. Bake until cheese is melted, bubbling, and lightly browned, about 4–6 minutes under the broiler or 8–10 minutes at 450°F. Watch carefully to prevent burning.

Carefully remove bowls from the oven (use oven mitts). Garnish with chopped parsley if desired and serve immediately. Warn diners that the bowls and soup will be very hot.