Classic French Onion Soup Gratinée

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A bistro classic from Paris: deeply caramelized onions simmered in a rich beef broth, ladled over toasted baguette and finished with a bubbling cap of melted Gruyère. The secret is patience with the onions and a generous gratin under the broiler.

Nutrition Facts

Per serving (estimated)

• 580 kcalCalories
• 28 gFat
• 15 gSaturated Fat
• 52 gCarbs
• 6 gFiber
• 18 gSugar
• 26 gProtein
• 1380 mgSodium
• 720 mgPotassium
• 460 mgCalcium
• 3.5 mgIron
• 16 mgVitamin C
• 320 mcgVitamin A

Ingredients

For the soup

• 3 lb (about 5 large) yellow onions, halved and thinly sliced
• 3 tbsp unsalted butter
• 1 tbsp olive oil
• 1 tsp granulated sugar
• 1/2 tsp fine sea salt, plus more to taste
• 1/2 cup dry white wine or dry sherry
• 6 cups (1.4 L) good-quality beef stock
• 2 tsp fresh thyme leaves (or 1 tsp dried)
• 1 bay leaf
• 1/2 tsp freshly ground black pepper
• 1 tbsp brandy or cognac (optional)

For the gratin topping

• 1 small baguette, cut into 8 thick slices
• 1 tbsp olive oil
• 2 cups (about 8 oz) grated Gruyère cheese
• 1/4 cup grated Parmigiano-Reggiano

Directions

1. Melt the butter with the olive oil in a large heavy pot or Dutch oven over medium-low heat. Add the sliced onions, sugar, and salt, and stir to coat. Cook gently, stirring every few minutes, for 35 to 45 minutes until the onions are a deep, mahogany brown; lower the heat if they begin to scorch.
2. Pour in the wine (or sherry) and scrape up any browned bits on the bottom of the pot. Let it bubble down for 2 minutes, then add the beef stock, thyme, bay leaf, and pepper. Simmer uncovered for 15 minutes to meld the flavors. Stir in the brandy, if using, taste and adjust salt.
3. Meanwhile, position an oven rack about 6 inches from the broiler and heat the broiler on high. Brush the baguette slices with olive oil and toast on a sheet pan under the broiler for 1 to 2 minutes per side until golden at the edges.
4. Ladle the hot soup into four oven-safe crocks or ramekins, filling each about three-quarters full. Float two toasted baguette slices on top of each crock, then blanket generously with the Gruyère and Parmigiano, making sure the cheese covers the bread and reaches the rim to seal.
5. Broil the crocks on the sheet pan for 3 to 5 minutes, watching closely, until the cheese is fully melted, bubbly, and spotted with deep golden brown. Let rest 2 minutes before serving (the bowls are extremely hot).

Cook’s Notes

• Patience is everything: true caramelization takes 35 to 45 minutes over medium-low heat. Rushing on high heat will burn the onions and turn the soup bitter.
• A homemade beef stock (or low-sodium store-bought) makes a huge difference here; avoid bouillon cubes, which can make the broth taste tinny.
• For the most authentic gratin, use Comté or Gruyère; Emmental is a fine substitute. A thin layer of cheese is not enough — pile it on so it forms a sealed, bubbling crust.
• Always toast the bread before floating it on the soup, or it will soak through and turn to mush under the broiler.
• Place the filled crocks on a sheet pan lined with parchment before broiling; the cheese inevitably melts over the edges and cleanup is much easier.

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