French Onion Soup Recipe

Prepare onions

Peel and thinly slice all onions so you have approximately 5 cups total sliced onions (about 3 cups yellow, 1 cup sweet, 1 cup red).

In a large heavy-bottomed pot or Dutch oven, heat the butter and 1 tablespoon olive oil over medium heat until butter foams. Add the sliced onions, sprinkle with 1 teaspoon salt and 1 teaspoon sugar (helps with caramelization), and stir to coat.

Cook the onions uncovered over medium to medium-low heat, stirring every 3–5 minutes. Allow them to soften and begin to brown. This process takes 35–45 minutes: patience is key. If onions begin to stick, reduce heat slightly and stir more frequently. The sugar and salt will encourage deep caramel color.

When onions are richly browned and jammy (deep golden to mahogany), add the freshly ground black pepper, thyme sprigs, and bay leaf. Cook for 1 minute to release herb aromas.

Increase heat to medium-high and add 1 cup dry white wine to deglaze the pot. Scrape up all browned bits from the bottom with a wooden spoon. Let the wine reduce by about half (2–3 minutes).

Stir in 2 cups beef demi-glace (or concentrated demi-glace dissolved in a small amount of warm water if needed) and 4 cups low-sodium beef broth. Add 1 teaspoon Worcestershire sauce.

Bring soup to a gentle simmer, reduce heat to low, and simmer uncovered for 20–25 minutes to let flavors meld. Taste and adjust seasoning with salt and pepper as needed. If using, stir in the 2 teaspoons sherry or brandy at the end of simmering.

Remove and discard thyme sprigs and bay leaf before serving or before ladling into bowls for broiling.

Preheat oven to 400°F (200°C) or use a broiler on medium-high. Arrange baguette slices on a baking sheet. Brush each slice lightly with the 1 tablespoon olive oil on top.

Toast baguette slices in the oven until golden and crisp, about 6–8 minutes, flipping once. Alternatively, broil 1–2 minutes per side—watch closely to avoid burning. Once toasted, rub the cut side of the halved garlic clove over each warm toast to impart subtle garlic flavor.

Pile a generous 2–3 tablespoons (or about 1/4–1/3 cup total cheese per crostini when assembling) of grated Swiss (or Swiss/Gruyère mix) on each crostini if making individual open-faced versions, or reserve cheese for topping bowls (see next section).

Preheat broiler (or set oven to highest broil setting). If using oven-safe bowls (ramekins or French onion soup crocks), preheat them briefly in the oven for 5 minutes to warm. Alternatively, use an ovenproof baking sheet for crostini.

Ladle hot soup into ovenproof bowls, filling to within about 1" of the rim. Float 1–2 toasted baguette slices on top of each bowl (or place a thick layer of cheese directly on top of soup). Generously top each bowl with a mound of grated Swiss cheese so it covers the bread and edges of the bowl.

Place bowls on a baking sheet and broil in the oven until cheese is fully melted, bubbling, and lightly browned at the edges, 2–4 minutes. Watch carefully to prevent burning.

Remove from oven and, if desired, sprinkle each bowl with the optional 1 tablespoon finely grated Parmesan and a pinch of chopped fresh parsley for color.

Serve the French onion soup immediately—hot and bubbling. Provide a spoon and a napkin per guest (cheesy lids can be very hot).

Leftover soup (without broiled cheese) can be refrigerated up to 3 days; reheat gently on the stovetop and re-toast crostini and re-broil cheese just before serving.