Baked French Onion Soup Recipe

Prepare onions

Peel and thinly slice the yellow onions to about 1/8" thickness so they caramelize evenly. Measure slices into cups (about 5 cups).

Caramelize onions

In a large, heavy-bottomed pot or Dutch oven, melt 2 tbs unsalted butter with 1 tbs olive oil over medium heat. Add the sliced onions and spread them into an even layer. Sprinkle 1 tsp kosher salt and 1 tsp sugar over the onions. Cook, stirring every 3–5 minutes, adjusting heat as necessary to maintain a steady gentle sizzle (not burning), until the onions are deep golden brown and richly caramelized — about 40–50 minutes. Use a wooden spoon to scrape up browned bits on the bottom as you stir.

Deglaze

When onions are deeply caramelized, raise heat to medium-high and add 1 cup dry white wine (or additional beef stock if not using wine). Scrape the bottom of the pot with a wooden spoon to deglaze and dissolve fond. Allow the wine to reduce by about half, roughly 3–5 minutes.

Simmer soup

Add 6 cups house-made beef stock, 2 bay leaves, 3 thyme sprigs (or 1 tsp dried thyme), and 1 tbs Worcestershire sauce. Bring to a gentle simmer, reduce heat to low, and simmer uncovered for 20 minutes to allow flavors to meld. Taste and adjust seasoning with additional salt and freshly ground black pepper if needed (about 1 tsp pepper called for in ingredients; adjust to taste). Remove and discard bay leaves and thyme stems before serving.

Prepare baguette rounds

Preheat oven to 375°F (190°C). Arrange 1/2" baguette slices (about 10 rounds) on a baking sheet. Brush both sides lightly with 2 tbs melted butter. If using, rub the cut side of the halved garlic clove over each toasted bread slice after baking for a subtle garlic note.

Toast bread

Bake the buttered slices until lightly golden and crisp, about 8–10 minutes, flipping once halfway. Remove and set aside.

Assemble cheese topping

Mix together 2 cups grated Gruyère and 1 cup finely grated Parmesan in a bowl. For each serving bowl, plan on a generous 1/3–1/2 cup cheese mixture so the soup will gratinate and form a golden crust.

Broil assembled bowls

Ladle the hot soup into oven-safe bowls, leaving about 1/2" headspace. Place one or two toasted baguette rounds on top of each bowl (or float them in the soup) and mound a generous layer of the Gruyère/Parmesan mixture over the bread so cheese contacts the soup surface. Place bowls on a baking sheet and broil in the oven on high (or 500°F/260°C) until cheese is melted, bubbling, and golden brown in spots, 2–5 minutes — watch carefully to avoid burning. Alternatively, use a kitchen torch to brown the cheese.

Remove the gratinéed bowls from the oven using oven mitts and let rest 1–2 minutes to cool slightly. Sprinkle 2 tbs thinly sliced fresh chives over the melted cheese. Serve immediately with extra toasted baguette on the side if desired.