Baked French Onion Recipe

Prepare onions

Peel and trim 6 medium yellow onions. Cut in half through the root, then slice thinly (about 1/8-inch) to yield roughly 6 cups when packed.

In a large, heavy-bottomed oven-safe pot or Dutch oven, melt 3 tbsp unsalted butter with 1 tbsp olive oil over medium heat. The oil raises the burn point and helps even browning.

Add the sliced onions, 1 tsp fine sea salt, and 1 tsp granulated sugar to the pot. Stir to coat, spread the onions in an even layer, and cook over medium to medium-low heat.

Caramelize the onions, stirring every 5–7 minutes and scraping up browned bits from the bottom. Adjust heat to keep them browning slowly without burning. This process takes 35–45 minutes until onions are deep golden-brown and jammy.

Once onions are deeply caramelized, increase heat to medium-high and add 1 cup dry white wine (or dry sherry). Scrape the bottom of the pot to deglaze and cook until the wine is mostly evaporated, about 2–3 minutes.

Stir in 1 tbsp tomato paste and cook 1 minute to deepen flavor. Add 3 cups low-sodium beef broth, 1 bay leaf, 2 sprigs fresh thyme, and 1 tsp freshly ground black pepper. Bring to a gentle simmer.

Reduce heat to low and simmer uncovered 15–20 minutes to concentrate flavors. Taste and adjust seasoning with additional salt if needed. Remove and discard the bay leaf and thyme stems (strip leaves if you kept them).

Preheat the oven to 425°F (220°C). If your pot is not oven-safe, transfer the soup to an oven-safe casserole or individual ovenproof bowls (ramekins).

Ladle soup into individual ovenproof bowls or leave in the Dutch oven. Place 1–2 toasted baguette slices on top of each portion, pressing lightly so they soak up some broth.

Combine 2 cups grated gruyère and 1 tablespoon grated parmesan. Heap a generous amount (about 1/4–1/2 cup) of the cheese mixture over the bread so it forms a thick covering.

Place bowls on a baking sheet and bake at 425°F (220°C) until cheese is melted, bubbling, and golden brown in spots, about 8–12 minutes. For a blistered top, you can finish under the broiler 1–2 minutes—watch closely to avoid burning.

Carefully remove bowls from oven (contents will be very hot). Garnish with 1 tbsp chopped fresh parsley per batch if desired. Serve immediately with additional crusty bread.