French Onion Recipe

Prepare onions

Peel and halve the onions, then cut into very thin slices (mandoline or sharp knife). Measure about 1.2 kg sliced onions.

Heat a large heavy-bottomed pot or Dutch oven over medium heat. Add the butter and oil and let the butter melt and foam without browning immediately.

Add the sliced onions and stir to coat with the butter-oil mixture. Cook uncovered, stirring frequently, for 10 minutes until softened.

Sprinkle the sugar, salt, and pepper over the onions. Continue to cook over medium-low heat, stirring every few minutes, for 35–45 minutes until the onions are deeply golden-brown and caramelized. Adjust heat as necessary to avoid burning; deglaze the bottom with a splash of stock or water if fond sticks too darkly.

If using, pour in the dry sherry or white wine to deglaze the pan, scraping up browned bits; let the alcohol cook off for 1–2 minutes.

Add the beef stock and chicken stock to the pot along with the bay leaves and thyme sprigs. Bring to a gentle simmer, then lower heat and simmer for 20 minutes to meld flavors. Taste and adjust seasoning with additional salt and pepper as needed. Remove and discard bay leaves and thyme sprigs (reserve extra thyme leaves for garnish).

Preheat the oven to 200°C (400°F) and position a rack in the center.

Arrange the baguette slices on a baking sheet. Brush each slice lightly with the melted butter and olive oil. Toast in the oven for 6–8 minutes until golden and crisp, flipping once for even browning.

Remove toasted slices and, while still warm, rub the cut side of the halved garlic clove over each slice for a hint of garlic flavor. Set aside.

Lower the oven temperature to 190°C (375°F) or prepare a broiler setting if using broiler to finish.

Ladle the hot soup into ovenproof crocks or bowls, leaving about 1/2 inch (1 cm) headspace. Float one or two toasted baguette slices on top of each bowl of soup (or place on a baking sheet to top afterward).

Combine the grated Gruyère and Parmesan (if using). Generously pile the cheese over the crouton so it will melt and form a gratin crust.

Place the bowls or baking sheet under the broiler or in the oven and cook until the cheese is bubbly, golden, and lightly browned at the edges, about 3–6 minutes depending on broiler strength. Watch carefully to avoid burning.

Remove the bowls from the oven using oven mitts. Sprinkle each bowl with chopped parsley, chives, and the reserved thyme leaves. Taste and add finishing salt and pepper to taste.

Serve immediately while the cheese is molten and the soup is hot. Provide a spoon to break through the cheesy crust and enjoy the layers of caramelized onion flavor.