French Onion Soup Gratinée Recipe

Prepare onions

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

In a large heavy-bottomed pot or Dutch oven, heat 1 tablespoon olive oil and 3 tablespoons unsalted butter over medium heat until butter melts and foams.

Add the sliced onions, 1 teaspoon sea salt, 1/2 teaspoon black pepper, and 1/2 teaspoon granulated sugar. Stir to coat and spread the onions evenly across the pan so they form an even layer.

Cook the onions gently, stirring every 3–5 minutes. Maintain a medium-low to medium heat so they soften and sweat without burning. After 20–25 minutes the onions should be very soft and beginning to brown at the edges.

Increase heat slightly to medium and continue to cook, stirring more frequently, until the onions are deep golden brown and caramelized, about 20–30 more minutes. If the pan starts to scorch, lower the heat and add a splash (1–2 tablespoons) of beef stock to deglaze and scrape up browned bits. Total caramelization time should be about 40–55 minutes.

When the onions are deeply caramelized, push them to the side and add 1/2 cup dry white wine or sherry (if using) to deglaze the pot. Scrape the fond from the bottom and let the wine reduce until nearly evaporated, about 2–3 minutes.

Stir in 1 tablespoon tomato paste and cook for 1 minute to remove raw flavor.

Add 6 cups beef stock, 2 bay leaves, 2 thyme sprigs, and 1 teaspoon Worcestershire sauce. Bring the soup to a gentle simmer, then lower heat and simmer, uncovered, for 20–25 minutes to meld flavors. Taste and adjust seasoning with additional salt and pepper as needed. If desired, stir in 1/2 teaspoon sherry vinegar to brighten flavors at the end.

Remove and discard bay leaves and thyme sprigs. Keep the soup hot while you prepare croutons and cheese.

Preheat the oven to 400°F (200°C). Arrange the thick bread slices on a baking sheet. Brush both sides lightly with 2 tablespoons olive oil or melted butter.

Toast the bread in the oven until golden and crisp, about 8–10 minutes, flipping once. If using, rub the warm toasted slices with the cut side of the garlic clove to impart a subtle garlic flavor.

Combine 2 cups grated Gruyère and 1/2 cup grated Comté/Emmental in a bowl. Season very lightly with 1/4 teaspoon freshly ground black pepper and toss to combine.

Ladle the hot soup into oven-safe bowls (about 1 to 1 1/2 cups soup per bowl). Place one thick crouton slice floating on each bowl so it fits the top.

Generously pile about 1/3 to 1/2 cup of the grated cheese mixture on top of each crouton, covering it and creating a cheese dome.

Set the bowls on a baking sheet and place under a preheated broiler set to high (or in a 450°F/230°C oven) about 4–6 inches from the heat source. Broil until the cheese is bubbly, deeply melted and developing golden-brown spots, about 2–4 minutes. Watch carefully to prevent burning.

Remove carefully (use oven mitts) and let rest 1–2 minutes. Sprinkle each bowl with a scant pinch of chopped fresh parsley, if using, and a crack of fresh pepper. Serve immediately.