French Onion Soup with Gruyere Croutons
French Onion Soup
A deeply savory French onion soup made with slow-caramelized onions, dry white wine, rich stock, toasted bread, and a bubbling Gruyere topping.
French onion soup earns its flavor slowly. The ingredient list is short, but the onions need enough time over moderate heat to turn from sharp and pale into a deep golden base that tastes sweet, savory, and concentrated.
A little flour gives the broth a gentle body, while dry white wine or vermouth lifts the richness of the stock. Beef stock gives the most traditional depth, but a strong mushroom stock works well when you want a meatless version with the same dark, rounded character.
The gratin topping is optional only in theory. Toasting the bread until firm keeps it from collapsing into the soup, and the cheese melts into both the broth and the crouton lid so every bowl has a brothy, crisp, and molten bite.
Use ovenproof bowls and a rimmed baking sheet for easier handling. The bowls come out very hot, so let them sit briefly before serving while the cheese is still bubbling.
Nutrition (per serving)
Directions
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1
Melt the butter with the olive oil in a 4- to 5-quart Dutch oven over medium-low heat. Add the sliced onions, toss well to coat, cover, and cook for 15 minutes until the onions have softened and released moisture.
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2
Uncover the pot, stir in the salt and sugar, and raise the heat to medium. Cook for 35 to 45 minutes, stirring often and scraping the bottom, until the onions are evenly deep golden brown and much reduced.
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3
Sprinkle the flour over the caramelized onions and cook for 3 minutes, stirring constantly, so the flour loses its raw taste and coats the onions lightly.
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4
Pour in the wine or vermouth and scrape up any browned bits. Add the stock gradually while stirring, then season with black pepper and a little more salt only if needed.
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5
Bring the soup to a simmer, reduce the heat to maintain gentle bubbling, and cook partially covered for 30 to 35 minutes. Skim the surface if needed and stir in the cognac or brandy at the end if using.
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6
While the soup simmers, heat the oven to 325°F. Arrange the toasted baguette slices on a baking sheet, brush lightly with melted butter, and warm until very dry and crisp.
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7
Set six ovenproof soup bowls on a rimmed baking sheet. Divide the hot soup among the bowls, then stir about 1/2 teaspoon grated raw onion and a small pinch of Gruyere into each bowl.
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8
Float two toasted baguette slices on each bowl and cover generously with the remaining Gruyere and Parmesan. Bake for 18 to 22 minutes, until the cheese is melted and the soup is bubbling at the edges.
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9
Switch the oven to broil and broil for 1 to 2 minutes, watching closely, until the cheese is browned in spots. Rest the bowls for 2 minutes, then serve carefully while hot.
Ingredients
- Yellow Onions, thinly sliced:1 1/2 pounds
- Unsalted Butter:3 tablespoons
- Olive Oil:1 tablespoon
- Kosher Salt:1 1/4 teaspoons
- Granulated Sugar:1/4 teaspoon
- All-Purpose Flour:3 tablespoons
- Dry White Wine or Dry Vermouth:1/2 cup
- Beef Stock or Robust Mushroom Stock:8 cups
- Freshly Ground Black Pepper:to taste
- Cognac or Brandy, optional:3 tablespoons
- Raw Onion, finely grated:1 tablespoon
- Gruyere or Swiss Cheese, grated:2 cups
- Parmesan Cheese, finely grated:1/3 cup
- Baguette Slices, toasted until dry and crisp:12 pieces
- Melted Butter, for brushing the toasts:1 tablespoon
Tips & Notes
- Do not rush the onion caramelization; pale onions will make a thin-tasting soup.
- If the onions begin to scorch before they are fully golden, lower the heat and add a tablespoon of stock to loosen the browned bits.
- Use low-sodium stock if possible so the final seasoning stays balanced after the cheese is added.
- For a vegetarian version, choose a dark mushroom stock and skip the optional cognac if preferred.
