French Onion Soup Recipe

Prepare onions

Peel the onions and cut them in half pole-to-pole. Thinly slice each half into 1/8- to 1/16-inch slices so they separate into long ribbons. Weigh or measure to about 2.5 lb total.

Caramelize onions

In a large heavy-bottomed pot or Dutch oven over medium heat, add the butter and olive oil. When the butter is melted and begins to foam, add the sliced onions, spread them evenly, and sprinkle with the sugar and 1/2 teaspoon of the salt. Stir to coat and cook, stirring every 3–5 minutes. Reduce heat to medium-low after 8–10 minutes if onions are browning too fast. Continue cooking, stirring more frequently as they begin to soften, for 35–45 minutes total until they are deeply golden brown and sweet. Scrape any fond from the bottom periodically to incorporate into the onions.

Deglaze

Increase heat to medium-high, add the white wine (if using) and use a wooden spoon to scrape any browned bits from the bottom of the pot. Let the wine reduce by about half, about 2–3 minutes. If not using wine, add a couple tablespoons of stock instead to deglaze.

Build the soup

Add the remaining 1/2 teaspoon salt, black pepper, beef bouillon paste (if using), bay leaves, thyme sprigs, Worcestershire sauce, and both stocks to the pot. Stir to combine, bring to a gentle simmer, then reduce heat to low. Cover slightly ajar and simmer gently for 20–25 minutes to meld flavors. Taste and add sherry or red wine vinegar and additional salt/pepper as needed to balance sweetness and deepen flavor.

Finish

Remove and discard thyme stems and bay leaves. If you prefer a clearer soup, skim any fat from the surface. Keep soup hot while you prepare the bread and cheese topping.

Prepare bread

Preheat the oven to 375°F (190°C). Butter one side of each baguette slice lightly. Arrange slices buttered-side-up on a baking sheet and toast in the oven until edges are golden and surfaces are lightly crisp, about 8–10 minutes. Alternatively, grill or pan-toast them. Set aside.

Assemble and brown

Ladle hot soup into ovenproof bowls or crocks, leaving about 1/2 inch from the top. Place one or two toasted baguette slices on top of each bowl, buttered side up, then heap a generous 1/4 to 1/3 cup of grated Gruyère and a sprinkle of Parmesan over the bread, covering the surface. Place bowls on a baking sheet.

Broil

Set oven to broil on high and position the rack 6–8 inches from the element. Broil the bowls until the cheese is fully melted, bubbling, and begins to brown in spots, about 2–4 minutes. Watch carefully to avoid burning.

Serve

Remove baking sheet from oven. Sprinkle with fresh thyme leaves and serve immediately with hot soup. Caution guests — bowls will be very hot.