French Onion Soup Recipe

Prepare onions

Peel and thinly slice onions into 1/4-inch slices (about 6 cups).

In a large, heavy-bottomed pot (6–8 quart), heat 1 tablespoon olive oil and 3 tablespoons unsalted butter over medium heat until butter foams.

Add the sliced onions and 1 teaspoon granulated sugar. Cook, stirring frequently, for 20–30 minutes until onions are deeply golden-brown and caramelized. Reduce heat if onions begin to burn; scrape browned bits from the bottom occasionally.

Sprinkle 1 tablespoon flour over the caramelized onions and cook, stirring, 1–2 minutes to remove raw flour taste. This will help thicken the soup slightly.

Deglaze the pot with 1 cup dry wine, scraping up all browned fond from the bottom. Let wine reduce by about half, 3–4 minutes.

Add 8 cups beef bone broth, 3 sprigs thyme, 2 bay leaves, 1 teaspoon kosher salt, and 1 teaspoon freshly ground black pepper. Bring to a simmer, then reduce heat to low and simmer gently, uncovered, for 25–30 minutes to meld flavors. Taste and adjust salt and pepper at the end. Remove thyme sprigs and bay leaves before serving.

Preheat oven to 425°F (220°C) with rack in middle position. Line a baking sheet with foil or parchment.

Slice the baguette into 1/2-inch slices (about 12–16 slices depending on loaf). Brush both sides lightly with 2 tablespoons melted butter.

Arrange slices on the prepared baking sheet. Toast in oven 6–8 minutes, flipping once, until golden and crisp. Alternatively, toast under the broiler for 1–2 minutes per side—watch carefully to avoid burning.

Remove toasts from oven and rub the cut side with halved garlic cloves while still warm to infuse garlic flavor. Set aside.

Ladle soup into oven-safe bowls (ramekins or French onion soup crocks), filling about 3/4 full. Place one or two garlic-toasted baguette slices on top of each bowl, then pile 1/3 to 1/2 cup grated Gruyère (or enough to fully cover bread and bowl rim) over each.

Sprinkle a light dusting of Parmesan over the Gruyère if using.

Place the bowls on a baking sheet and transfer to the oven set to broil (or 500°F/260°C). Broil 2–4 minutes until cheese is melted, bubbling, and golden-brown. Watch closely to prevent burning. Alternatively, use a kitchen torch to brown the cheese evenly.

Carefully remove hot bowls from oven using oven mitts. Drizzle about 1/4 teaspoon to 1 teaspoon truffle oil per bowl (use less for a subtle truffle note).

Garnish each bowl with about 1 teaspoon chopped fresh parsley. Serve immediately with an extra toasted baguette slice on the side if desired.