French Onion Soup Recipe

Prepare onions

Peel and thinly slice 2 lbs of yellow onions into even slices (about 1/8" thick). Aim for consistent width so they caramelize evenly.

Sweat and caramelize

In a large, heavy-bottomed pot or Dutch oven, heat 1 tablespoon olive oil and 3 tablespoons unsalted butter over medium heat until butter foams. Add sliced onions, 1 teaspoon salt, and 1 teaspoon sugar. Stir to coat. Cook, stirring every 3–5 minutes, reducing heat as needed to prevent burning. After 20–30 minutes the onions will be softened and beginning to caramelize; continue cooking 15–25 more minutes until deep golden brown and jam-like. If onions begin to stick or brown too fast, lower the heat and stir more frequently.

Add garlic and deglaze

Add 1 minced garlic clove and cook 30 seconds until fragrant. Increase heat to medium-high and add 1 cup dry white wine (or dry sherry) to deglaze, scraping up browned bits from the bottom of the pot. Let the wine reduce by about half, about 2–4 minutes.

Build the broth

Stir in 1 tablespoon tomato paste and cook 1 minute. Add 6 cups beef stock and 2 cups chicken stock (or additional beef stock), 3 sprigs fresh thyme, and 1 bay leaf. Bring to a gentle simmer. Reduce heat to low and simmer, partially covered, for 25–30 minutes to let flavors meld. Taste and season with freshly ground black pepper (about 1 teaspoon) and additional salt if needed. Remove and discard thyme sprigs and bay leaf. Stir in 2 teaspoons dry sherry if using, then keep the soup warm while preparing croutons and cheese.

Prepare baguette slices

Preheat oven to 375°F (190°C). Slice the baguette into 1/2-inch thick slices and arrange in a single layer on a baking sheet.

Make garlic butter

In a small bowl, combine 3 tablespoons melted unsalted butter, 1 tablespoon olive oil, 2 minced garlic cloves, 1 tablespoon finely chopped parsley, and 1 teaspoon coarse sea salt. Stir to combine.

Brush and toast

Brush both sides of each baguette slice with the garlic-butter mixture. Toast in the preheated oven until golden and crisp, about 8–10 minutes, flipping once halfway through. Remove and set aside. For slightly softer croutons meant to be floated on the soup, toast 4–6 minutes instead of 8–10.

Preheat broiler and portion soup

Preheat the oven broiler on high. Ladle the hot soup into oven-safe bowls or crocks, filling them about 3/4 full (leave room for crouton and cheese).

Top with crouton and cheese

Place one or two garlic baguette slices on top of each bowl of soup (centered). Sprinkle about 1/2 to 3/4 cup grated Gruyère over the crouton and exposed soup surface, pressing slightly so cheese melts and adheres. If using, sprinkle 1 tablespoon grated Parmesan across the bowls.

Broil until bubbly

Place bowls on a baking sheet and broil on the top oven rack 3–6 inches from the heat source. Broil 2–4 minutes, watching closely, until cheese is melted, bubbling, and lightly browned. Rotate tray as needed for even browning. Remove carefully—bowls will be hot.

Serve

Let cool for 2 minutes, garnish with a pinch of fresh thyme leaves if desired, and serve immediately with additional baguette slices on the side.