French Onion Soup Recipe

Prepare onions

Peel and halve onions from root to tip. Place cut side down and slice thin (about 1/8 inch) to yield long, even strips. Aim for about 2 pounds total sliced onions.

In a large, heavy-bottomed Dutch oven or wide saucepan, melt the butter with the olive oil over medium heat until butter foams but does not brown.

Add all sliced onions to the pot and stir to coat evenly with the butter-oil mixture. Spread onions into an even layer and cook over medium heat for 10 minutes, stirring occasionally to prevent sticking.

After 10 minutes, reduce heat to medium-low. Add the granulated sugar and 1/2 teaspoon of the salt to help the onions caramelize evenly. Continue to cook, stirring every 5–8 minutes, scraping browned bits from the bottom. This caramelization will take 35–45 minutes total (up to 50 minutes for deeper color). Do not rush with higher heat or onions may burn.

When onions are deeply golden brown and sweet, sprinkle the tablespoon of flour over them and cook, stirring, for 1–2 minutes to remove the raw flour taste. This will slightly thicken the soup.

Increase heat to medium-high and carefully add the white wine to deglaze the pan, scraping up all browned fond from the bottom. Allow wine to simmer 2–3 minutes until mostly reduced.

Add the 6 cups of beef stock, the optional bouillon paste if using, the remaining 1/2 teaspoon salt, black pepper, thyme sprigs, and bay leaves. Bring to a gentle simmer, then reduce heat and simmer uncovered for 20–25 minutes to meld flavors. Taste and adjust seasoning; add the optional 2 tablespoons sherry or cognac at the end if desired. Remove thyme sprigs and bay leaves before serving.

While the soup simmers for its final 20–25 minutes, preheat the oven to 400°F (200°C) and line a baking sheet with parchment.

Brush both sides of baguette slices lightly with the 2 tablespoons extra-virgin olive oil. Place slices in a single layer on the baking sheet and toast in the oven 6–8 minutes, flipping once, until golden and crisp. For added garlic flavor, rub the warm toasts with the cut garlic clove after toasting.

Increase oven temperature to broil (or 475°F/245°C if broiler is not available). Ladle the hot soup into ovenproof bowls or crocks, leaving about 1/2 inch headspace. Place one or two toasted baguette slices on top of each bowl, then pile about 1/3 to 1/2 cup grated Gruyère (or enough to fully cover the toast). Sprinkle a little grated Parmesan if using.

Place bowls on a baking sheet and broil 2–4 inches from the broiler element for 2–5 minutes, watching closely, until cheese is bubbly and deeply golden with some brown spots. Alternatively, bake at 475°F (245°C) for 6–8 minutes until cheese melts and browns.

Carefully remove from oven (use oven mitts), let cool 2 minutes, then serve hot. Caution: bowls will be very hot.