French Onion Soup Recipe

Prepare onions

Peel and thinly slice enough yellow onions to yield about 6 cups (roughly 4–6 medium onions). Aim for consistent slices about 1/8-inch thick so they caramelize evenly.

Melt fat and sweat 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 the sliced onions, 1 teaspoon kosher salt and 1 teaspoon granulated sugar (the sugar helps caramelization). Stir to coat and spread onions in an even layer.

Caramelize onions

Cook the onions over medium to medium-low heat, stirring every 4–6 minutes. After 15–20 minutes the onions will be soft and beginning to brown at edges; reduce heat if they sizzle or stick. Continue cooking and stirring periodically for 30–40 minutes total until deep golden-brown and jammy. Scrape pan brown bits into the onions. If the pan becomes dry or onions threaten to burn, add a tablespoon of water and deglaze the bottom.

Add flour

Once onions are richly browned, sprinkle 1 tablespoon all-purpose flour over them and stir for 1–2 minutes to remove raw flour taste. This will slightly thicken the broth.

Deglaze with wine

Raise heat to medium-high and pour in 1 cup dry white wine (or omit and use an equal amount of stock). Use a wooden spoon to scrape any browned bits from the pot. Let the wine reduce by half, about 2–3 minutes.

Add stock and aromatics

Add 6 cups beef stock, 2 bay leaves, 3 sprigs fresh thyme and 1 teaspoon Worcestershire sauce. Bring to a gentle simmer, then reduce heat to low. Simmer uncovered for 20–30 minutes to meld flavors. Taste and adjust seasoning with salt and freshly ground pepper (start with an additional 1/2 teaspoon salt if needed). Remove and discard thyme stems and bay leaves before serving.

Prepare bread and cheese

While the soup simmers, preheat oven to broil (or 225°C/425°F if toasting). Arrange baguette slices on a baking sheet, brush lightly with olive oil if desired, and toast under the broiler until golden on both sides, about 1–2 minutes per side. Scatter 2 cups grated Gruyère and 1 tablespoon grated Parmesan onto each toast, or hold the cheese to melt directly on bowls as described below.

Assemble and gratinate (individual bowls)

Preheat oven broiler. Ladle hot soup into ovenproof bowls, leaving ~1/2-inch headspace. Place one or two toasted baguette slices on top of each bowl (or float if you prefer), evenly sprinkle 1/4–1/3 cup Gruyère (plus a little Parmesan) over the bread and soup to cover. Place bowls on a baking sheet and broil 2–4 minutes until the cheese is melted, bubbling and lightly browned. Watch carefully to avoid burning.

Alternative: French onion in ovenproof crocks

If you prefer deeper gratin, place bowls under broiler for up to 5 minutes until cheese has a golden crust. Remove carefully with oven mitts; plate on warmed saucers to protect surfaces.

Finish and serve

Let bowls rest 1–2 minutes after broiling to cool slightly. Garnish with a small thyme leaf if desired. Serve immediately; warn diners the bowls and cheese will be hot.