French Onion Soup Recipe

Prepare onions

Peel and halve the onions, then thinly slice each into half-moons so you have roughly 2 lbs of sliced onion.

Sweat and caramelize

In a large heavy-bottomed pot or Dutch oven, heat the butter and olive oil over medium heat until butter melts and begins to foam. Add the sliced onions, sprinkle with the salt and sugar, and stir to coat. Cook, stirring every 2–3 minutes, reducing heat as needed to maintain a steady gentle simmer. Continue to cook for 35–45 minutes until the onions are deeply golden-brown and caramelized. If they begin to stick excessively, deglaze the pan with a tablespoon of water and scrape up browned bits.

Deglaze

Increase heat to medium-high, add the white wine (if using) and cook, scraping the bottom, until the wine has mostly evaporated, about 2–3 minutes.

Simmer soup

Add the beef stock, bay leaves, thyme sprigs, Worcestershire sauce, sherry or brandy (if using), and freshly ground black pepper. Bring to a gentle simmer, then reduce heat to low. Simmer, uncovered, for 20–25 minutes to let the flavors meld. Taste and adjust seasoning with additional salt and pepper if needed. Remove and discard the thyme sprigs and bay leaves.

Toast baguette slices

Preheat the broiler. Brush both sides of baguette slices lightly with olive oil or melted butter. Arrange on a baking sheet and toast under the broiler until golden-brown on both sides, about 1–2 minutes per side. Watch carefully to avoid burning.

Assemble soup bowls

Ladle the hot soup into oven-safe bowls or crocks, placing one or two toasted baguette slices on top of each portion (they should float or be partially submerged). Sprinkle a generous handful of grated Gruyère over each bowl, finishing with a little grated Parmesan if using.

Melt cheese

Place the bowls on the baking sheet and slide under the broiler until the cheese is bubbling and golden-brown, 2–4 minutes. Remove carefully — bowls will be very hot. Let sit 1–2 minutes before serving to set slightly.