French Onion Soup Recipe

Prepare onions

Peel and thinly slice 2 lb of yellow onions into half-moon slices about 1/8-inch thick. Aim for uniform slices so they caramelize evenly.

Cook onions

In a large heavy-bottomed pot or Dutch oven, heat 4 tbsp unsalted butter and 1 tbsp olive oil over medium heat until butter melts and begins to foam. Add the sliced onions, 1 tsp kosher salt, 1/2 tsp freshly ground black pepper, and 1/2 tsp granulated sugar (the sugar helps with even caramelization). Stir to coat the onions in fat.

Caramelize

Reduce heat to medium-low. Cook the onions, stirring every 5 minutes, scraping the browned bits from the bottom of the pot with a wooden spoon. Continue for 35–50 minutes until the onions are deeply golden-brown and very soft. If the pan dries out or starts to scorch, add a tablespoon or two of water and continue cooking. Adjust heat as needed to prevent burning.

Deglaze

Once the onions are richly caramelized, increase heat to medium-high and sprinkle 1 tbsp all-purpose flour over the onions. Cook for 1–2 minutes, stirring, to remove raw flour taste. Pour in 3/4 cup dry white wine to deglaze, scraping up all browned bits from the bottom. Let the wine reduce by half, about 2–3 minutes.

Add stock and aromatics

Add 6 cups beef stock, 2 tbsp dry sherry or brandy (if using), 2 bay leaves, and 2 sprigs fresh thyme. Bring to a simmer, then reduce heat to low and simmer gently, uncovered, for 20–30 minutes to let flavors meld. Taste and season with additional salt and pepper as needed. Remove and discard thyme sprigs and bay leaves before serving.

Toast baguette slices

Preheat oven to 400°F (200°C) or set broiler to medium-high. Brush both sides of 8 baguette slices with 1 tbsp olive oil and place on a baking sheet. Toast in the oven for 5–8 minutes or under the broiler for 1–2 minutes per side until golden and crisp. Remove and rub the warm toasts with the cut side of 1 garlic clove for a subtle garlic flavor.

Assemble and melt cheese

Ladle the hot soup into oven-safe bowls (leave about 1/2-inch headspace). Place one or two toasted baguette slices on top of each bowl of soup. Top generously with grated Gruyère (about 1/4 cup to 1/2 cup per bowl) and a light sprinkle of Parmesan if using. Place the bowls on a baking sheet and put under the broiler until the cheese is melted, bubbling, and golden brown, about 2–4 minutes. Watch closely to avoid burning.

Serve

Carefully remove hot bowls from oven (use oven mitts). Let cool for 1–2 minutes, garnish with a small thyme leaf if desired, and serve immediately.