French Onion Recipe

Prepare onions

Peel and cut the yellow onions in half from root to tip. Thinly slice each half into 1/8-1/4-inch slices so they cook evenly.

Caramelize onions

Heat a large heavy-bottomed pot or Dutch oven over medium heat. Add the butter and olive oil and allow the butter to melt and foam but not brown. Add the sliced onions, sprinkle with the fine sea salt and the granulated sugar. Stir to coat. Cook, stirring every 3-5 minutes to prevent burning, adjusting heat as necessary, for 35-45 minutes until the onions are deeply golden brown and soft. If the pan dries or onions start to stick, add a tablespoon or two of water to deglaze and continue cooking. The goal is deep, sweet caramelization — patience is key.

Deglaze

Once the onions are richly browned, increase heat to medium-high and add the white wine (or vermouth). Scrape the bottom of the pot with a wooden spoon to lift any browned bits. Reduce the wine by about half, about 3-5 minutes.

Build the soup

Add the beef stock and optional chicken stock to the pot along with the thyme sprigs, bay leaves, Worcestershire sauce, and freshly ground black pepper. Stir to combine and bring to a gentle simmer. Taste and adjust salt if necessary (remember the cheese and stock can add salt later).

Simmer

Lower heat so the soup barely simmers and cook, uncovered, for 20-30 minutes to allow flavors to meld. If using, stir in the optional dry sherry in the last 2 minutes of simmering. Remove thyme sprigs and bay leaves before serving.

Prepare crostini

While the soup simmers, preheat the oven to 375°F (190°C). Arrange baguette slices on a baking sheet. Brush each lightly with the 2 tsp olive oil. Toast for about 8-10 minutes until golden and crisp, flipping once. When the slices are hot, rub the cut side of the garlic clove over each slice for a hint of garlic flavor.

Assemble gratinée

Ladle the hot soup into oven-safe bowls. Place one or two crostini on top of each bowl, then generously sprinkle grated Gruyère over the bread so it covers and drapes slightly into the broth. Add a light sprinkle of grated Parmesan if using.

Broil to melt cheese

Set the oven to broil. Place the bowls on a baking sheet and broil until the cheese is bubbling and golden brown in spots, 2-4 minutes — watch closely to avoid burning. Alternatively, if you have an oven-safe ladle or a salamander, use that for a shorter, hotter melt.

Remove bowls from the oven carefully (they will be very hot). Garnish with a small drizzle of optional dry sherry and a sprinkle of freshly chopped parsley if desired. Serve immediately with extra crostini on the side.