Traditional French Onion Soup Recipe

Prepare onions

Peel and thinly slice onions to yield about 6 cups. Use a sharp knife or mandoline for even slices.

In a large heavy-bottomed pot or Dutch oven over medium heat, melt the butter with the olive oil until foaming.

Add all sliced onions to the pot, stir to coat with butter and oil. Sprinkle sugar and 1 tsp salt over the onions (this helps with caramelization).

Cook the onions over medium to medium-low heat, stirring frequently, for 35–45 minutes. Adjust heat as needed so onions soften and slowly caramelize without burning. Scrape browned bits off the bottom with a wooden spoon while stirring.

When onions are deeply golden-brown and sweet (not bitter), increase heat to medium-high and add the white wine to deglaze the pot, scraping up fond from the bottom. Let the wine reduce by about half, 2–4 minutes.

Add the beef stock, bay leaves, thyme sprigs, and Worcestershire sauce. Bring to a gentle simmer, reduce heat to low, and simmer, uncovered, for 20–25 minutes to let flavors meld. Taste and adjust seasoning with additional salt and pepper as needed. Remove and discard bay leaves and thyme stems before serving.

While soup simmers, preheat the oven to 400°F (200°C). Arrange baguette slices on a baking sheet.

Brush each slice lightly with olive oil on one side. Toast in the preheated oven until edges are golden, about 6–8 minutes. Flip if necessary for even toasting.

Remove toasted slices and rub the cut side of halved garlic cloves over the top of each warm toast to impart garlic flavor.

Assembly option A — Oven-safe bowls

Preheat broiler. Ladle hot soup into oven-safe bowls, leaving 1/2-inch headspace. Place 1 or 2 garlic-rubbed toasts on top of each bowl of soup. Pile 1/3 to 1/2 cup of grated Gruyère (and a sprinkle of Parmesan, if using) over the bread, covering edges. Place bowls on a baking sheet and broil 3–5 minutes until cheese is bubbling and golden. Remove carefully and garnish with chopped parsley if desired.

Assembly option B — Sheet-pan melt (for non-oven-safe bowls)

Ladle hot soup into oven-safe small crocks or serve bowls that are oven-safe; if bowls are not oven-safe, place soup in bowls and set oven-safe ramekins or shallow dishes on a sheet pan. Place garlic toasts on baking sheet, top each with soup-safe amount of cheese, and melt under broiler until bubbly and browned. Transfer cheese-topped toasts to float on bowls of soup immediately before serving.

Serve immediately while cheese is melted and soup is hot. Caution guests that bowls will be very hot.