French Onion Soup Recipe

Prepare onions

Peel and thinly slice enough yellow onions to yield about 6 cups when sliced. Separate slices into strands so they cook evenly.

Heat a large heavy-bottomed pot or Dutch oven over medium heat. Add the butter and olive oil and let the butter melt and foam but not brown.

Add the sliced onions to the pot and stir to coat with fat. Cook over medium heat, stirring frequently, until the onions soften (about 10 minutes).

Reduce heat to medium-low. Sprinkle the onions with the sugar, salt, and pepper. Continue to cook, stirring every few minutes, until the onions are a deep golden brown and caramelized, about 40–50 minutes total from when you started (adjust heat as needed to prevent burning).

Once caramelized, increase heat to medium-high and deglaze the pot with the dry white wine, scraping up any browned bits from the bottom. Let the wine reduce by about half, 3–4 minutes.

Add the beef stock and chicken stock to the pot, along with the thyme sprigs, bay leaf, and Worcestershire sauce. Bring to a simmer, then reduce heat to low and gently simmer uncovered for 20–25 minutes to marry flavors.

Taste and adjust seasoning with salt and pepper. If using, stir in the optional 2 tablespoons sherry or brandy at the end of simmering, then remove thyme sprigs and bay leaf before serving.

While the soup simmers, preheat the oven to 375°F (190°C).

Arrange the baguette slices on a baking sheet. Brush both sides lightly with the 2 tablespoons extra-virgin olive oil. Toast in the oven until golden and crisp, about 8–10 minutes, flipping once. Remove and while still warm, rub the cut side of the halved garlic clove over one side of each toast for a hint of garlic flavor.

Combine the grated Gruyère and grated Parmesan in a bowl and toss lightly so the cheeses are evenly mixed.

Ladle the hot soup into oven-safe bowls (about 1 to 1 1/2 cups soup per bowl). Place 1–2 toasted baguette slices on top of each bowl of soup (you can also float them on the surface). Generously mound the cheese mixture over the bread so it covers and slightly spills over the rim.

Place the bowls on a baking sheet and transfer to the oven (or under a broiler set to high, 6 inches from the heat). Broil until the cheese is melted, bubbly, and golden brown in spots, 3–5 minutes under a broiler or 10–12 minutes at 375°F. Watch carefully to avoid burning.

Remove from the oven and let cool for 2 minutes. Grind a little black pepper over the top if desired.

If not added earlier, stir the optional sherry or brandy into the soup just before ladling for an aromatic lift.

Garnish each bowl with a sprinkle of chopped fresh parsley if using. Serve immediately while piping hot.