Baked French Onion Soup Recipe

Prepare onions

Peel and thinly slice onions to about 1/8" thickness so they will caramelize evenly. Measure approximately 3 packed cups of sliced onions.

In a large, heavy-bottomed pot or Dutch oven, melt butter with olive oil over medium heat. When the butter foams, add the sliced onions, sprinkle with the sugar and 1/2 teaspoon of the kosher salt (reserve remaining salt for later), and stir to coat.

Cook the onions over medium to medium-low heat, stirring frequently (every 2–3 minutes). Allow them to slowly soften and begin to brown; this will take about 30–40 minutes. If they start to stick, lower the heat and stir more often. Aim for deep golden-brown color without burning.

When the onions are richly caramelized, stir in the remaining 1/2 teaspoon kosher salt, 1/2 teaspoon black pepper, and 1 tablespoon flour. Cook for 1–2 minutes to remove the raw flour taste and to help thicken the base.

Add the white wine or sherry (if using) and scrape up any browned bits from the bottom of the pot with a wooden spoon. Allow the alcohol to reduce for 1–2 minutes.

Pour in the beef stock and optional consommé, add the bay leaf and thyme sprigs, and stir in the Worcestershire sauce. Increase heat to bring the soup to a gentle boil, then reduce to a simmer. Simmer uncovered for 20–25 minutes to meld flavors. Taste and adjust seasoning with remaining salt and pepper as needed. Remove and discard bay leaf and thyme stems before serving.

While the soup simmers, preheat the oven to 425°F (220°C). Arrange baguette slices on a baking sheet and toast in the oven until lightly golden, about 5–7 minutes. Alternatively, toast under the broiler, watching carefully to avoid burning.

Place 4–6 ovenproof crocks or ramekins on a rimmed baking sheet. Ladle the hot soup into each dish, leaving about 1/2" headspace so it won't bubble over when baked.

Place one or two toasted bread slices on top of each soup-filled crock. Divide the grated Gruyère and Parmesan evenly over the bread so each bowl has a generous, even layer. Finish with a light crack of black pepper (about 1/8–1/4 tsp per bowl total).

Bake in the preheated oven for 8–12 minutes until the cheese is melted and bubbling. For a deeply browned, blistered top, switch the oven to broil and broil 1–2 minutes more, watching closely to prevent burning.

Remove the baking sheet from the oven and let the crocks sit 2–3 minutes to settle. Sprinkle chopped parsley over each bowl for color and serve hot. Warn diners that the bowls will be very hot.