French Onion Soup Recipe

Prepare onions

Peel and halve the yellow onions. Slice them crosswise into very thin half-moons (about 1/8-inch). Aim for uniform slices so they caramelize evenly.

Sweat and caramelize onions

In a large, heavy-bottomed pot or Dutch oven, heat 4 tbs unsalted butter and 1 tbs olive oil over medium heat until the butter foams. Add the sliced onions, 1 tsp sea salt and 1/2 tsp freshly ground black pepper. Cook, stirring every few minutes, until the onions soften (about 15 minutes). Sprinkle 1/2 tsp granulated sugar over the onions to encourage browning. Continue cooking over medium-low heat, stirring more frequently and scraping the bottom to prevent sticking, until deep golden brown and richly caramelized, 30–40 more minutes. Do not rush this step — proper caramelization is key to flavor.

Deglaze

Raise the heat to medium-high and add 1/2 cup dry white wine (or a splash of stock if not using wine). Scrape up the browned bits from the bottom of the pot with a wooden spoon. Cook until the wine reduces by about half, 2–3 minutes.

Simmer the soup

Add 6 cups beef stock, 2 bay leaves, 3 thyme sprigs, and 1 tsp Worcestershire sauce. Bring to a gentle simmer, then reduce heat to low and simmer, partially covered, for 20–25 minutes to marry flavors. Taste and adjust seasoning with additional salt and pepper if needed. Remove and discard the bay leaves and thyme sprigs before serving.

Prepare baguette slices

Preheat oven to 375°F (190°C). Slice the baguette into 1/2-inch thick rounds. Arrange slices on a baking sheet. Brush both sides lightly with 2 tbs olive oil and sprinkle with 1/4 tsp coarse salt. Toast in the oven until lightly golden and crisp, 8–10 minutes, flipping once halfway. Optional: rub one side of each warm toast with the halved garlic clove for a subtle garlic note.

Assemble croûtes

Ladle hot soup into ovenproof bowls (or a large shallow ovenproof casserole for family-style). Place one or two toasted baguette slices on top of each bowl of soup, or place them on a tray if finishing under a broiler. Generously mound about 1/4 to 1/2 cup grated Gruyère (approximately 2 cups total divided) over each bowl so the cheese covers the bread and forms a thick layer. Sprinkle a little Parmesan on top if using.

Brown the cheese

Set the bowls on a baking sheet and place under a preheated broiler on high, about 4–6 inches from the heat, until the cheese is bubbly and deeply golden-brown in spots, 3–5 minutes. Watch closely to prevent burning. Alternatively, bake at 400°F (200°C) for 8–12 minutes until cheese is melted and starting to brown.

Remove bowls from oven carefully (they will be very hot). Sprinkle with chopped fresh parsley or extra thyme for garnish. Let cool 2–3 minutes — the soup will be extremely hot. Serve immediately with an extra toasted baguette on the side.