French Onion Soup Recipe

Prepare onions

Peel and thinly slice enough yellow onions to yield about 6 cups (about 3 large onions).

Caramelize onions

In a large heavy-bottomed pot or Dutch oven, heat 1 tablespoon olive oil and 3 tablespoons unsalted butter over medium heat until butter foams. Add the sliced onions, 1 teaspoon salt, and 1 teaspoon granulated sugar. Stir to coat and spread into an even layer. Cook, stirring every 4–5 minutes, lowering heat if onions are browning too quickly. Continue for 35–45 minutes until onions are deeply golden-brown and sweetly caramelized. Scrape browned bits from the bottom as needed.

Add aromatics and deglaze

When onions are deeply caramelized, add 1 tablespoon fresh thyme (or 1/2 teaspoon dried thyme) and 2 bay leaves. Increase heat to medium-high and add 1 cup dry white wine (optional) to deglaze, scraping up browned bits. Let the wine reduce by about half, 2–3 minutes. Add 2 tablespoons brandy and let it bubble for 30–60 seconds to burn off the alcohol and concentrate flavor.

Add stock and simmer

Pour in 6 cups beef stock, add 1 teaspoon Worcestershire sauce and 1 teaspoon freshly ground black pepper. Bring to a gentle simmer, reduce heat to low, and simmer uncovered for 20–30 minutes to develop flavor. Taste and adjust seasoning with extra salt and pepper to taste. Remove and discard bay leaves.

Prepare crostini

Preheat oven to 375°F (190°C). Arrange 1/2-inch slices of baguette on a baking sheet. Brush lightly with 1 tablespoon olive oil. Toast in the oven for 8–10 minutes until crisp and golden. Rub each warm toast with the cut side of the garlic clove to impart a subtle garlic flavor.

Assemble cheese topping

Mix 2 cups grated aged Swiss cheese with 1 tablespoon grated Parmesan. Pile a generous amount of the cheese mixture onto each crostini or place the toasted crostini on top of ovenproof soup bowls.

Broil to melt

If using oven-safe bowls: ladle hot soup into individual ovenproof bowls, place a cheese-covered crostini on top of each bowl or float crostini slices in the soup and sprinkle remaining cheese over the bowl. Place bowls on a baking sheet and broil 3–5 inches from the broiler for 2–4 minutes until cheese is bubbly and deeply golden (watch carefully to avoid burning). If using a baking sheet: put cheese-topped crostini under the broiler until cheese is melted and browned, then float on top of bowls of soup.

Remove bowls from the oven using oven mitts. Sprinkle each serving with a pinch of chopped fresh parsley and, if desired, a small extra grind of black pepper. Serve immediately with remaining crostini on the side.