French Onion Soup Recipe

Prepare onions

Peel and thinly slice all onions and shallots into uniform 1/8- to 1/4-inch slices so they caramelize evenly. Measure slices into cups to confirm quantities.

Begin cooking

In a large heavy-bottomed pot or Dutch oven over medium heat, melt the butter with the 1 tbsp olive oil until foaming subsides. The oil raises the smoke point so the butter doesn't burn.

Caramelize onions

Add all sliced onions and shallots to the pot, stir to coat in butter/oil, then spread them into an even layer. Sprinkle 1 tsp granulated sugar and 1.5 tsp kosher salt over the onions. Cook over medium-low to medium heat, stirring every 5–7 minutes, scraping up any fond from the bottom. Continue to cook for 40–55 minutes until the onions are a deep golden brown and sweet — lower heat if they begin to burn and increase stirring frequency.

Deglaze

Increase heat to medium-high, add 1 cup dry white wine and use a wooden spoon to scrape any browned bits from the bottom of the pot. Let the wine reduce by about half, 3–5 minutes, to concentrate flavor and evaporate alcohol.

Add stocks and aromatics

Add 6 cups beef stock and 1 cup chicken stock to the pot along with 2 bay leaves, 3 sprigs fresh thyme, 1 tsp Worcestershire sauce, and 1 tsp freshly ground black pepper. Bring to a gentle simmer, then reduce heat to maintain a low simmer. Simmer uncovered for 20–30 minutes to meld flavors. Taste and adjust seasoning with salt if needed.

Finish soup (optional cognac)

Remove and discard the bay leaves and thyme stems. If using, stir in 2 tbsp cognac or brandy off the heat for added depth. Keep soup hot while you prepare toasts and cheese.

Prepare bread

Preheat oven to 400°F (200°C). Arrange sourdough slices on a baking sheet. Lightly brush both sides with 1 tbsp olive oil.

Toast bread

Bake the slices in the preheated oven 6–8 minutes, flip, and bake another 4–6 minutes until edges are lightly golden and the slices are crisp but not hard. Remove and set aside.

Assemble crocks (if using ovenproof bowls)

Ladle hot soup into individual ovenproof bowls or crocks, leaving about 1/2 inch headspace. Place one or two toasted sourdough slices on top of each bowl of soup, then mound generously with grated Gruyère (about 1/3 to 1/2 cup per bowl). Sprinkle a little grated Parmesan on top if using.

Broil to melt cheese

Switch oven to broil on high (or set salamander) and position rack 6–8 inches from heat. Place filled bowls on a baking sheet and broil until cheese is bubbling and browned in spots, 2–5 minutes — watch carefully to avoid burning. Alternatively, use a kitchen torch to melt and brown the cheese evenly.

Serve

Carefully remove hot bowls from oven (use oven mitts). Garnish with a pinch of fresh thyme leaves. Serve immediately with extra toasted sourdough on the side.

If making soup in a large pot to ladle into bowls instead of broiling in individual crocks, place a toasted slice and grated Gruyère on a baking sheet and broil just until cheese melts and browns; then slide the cheese-topped toast onto each bowl of soup. Serve garnished with fresh thyme.