📝 About This Recipe
Born in the bustling markets of Les Halles, this quintessential French classic is the ultimate soul-warming comfort food. Our version features deeply caramelized yellow onions simmered in a rich, sherry-spiked beef bone broth, topped with crusty sourdough and a bubbling crown of nutty Gruyère cheese. It is a masterclass in patience and technique, transforming humble ingredients into a sophisticated symphony of sweet and savory flavors.
🥗 Ingredients
The Onion Base
- 3 pounds Yellow Onions (about 5-6 large onions, thinly sliced pole-to-pole)
- 4 tablespoons Unsalted Butter (high-quality European style preferred)
- 1 tablespoon Extra Virgin Olive Oil
- 1/2 teaspoon Granulated Sugar (to assist with caramelization)
- 1 teaspoon Kosher Salt (plus more to taste)
The Broth and Aromatics
- 1/2 cup Dry Sherry (can substitute with dry white wine or Vermouth)
- 6 cups Beef Bone Broth (low sodium, high quality)
- 3 pieces Garlic Cloves (minced)
- 2 tablespoons All-Purpose Flour (to slightly thicken the consistency)
- 4 pieces Fresh Thyme Sprigs (tied with kitchen twine)
- 1 piece Bay Leaf (dried)
- 1/2 teaspoon Black Pepper (freshly cracked)
- 1 teaspoon Balsamic Vinegar (for a final touch of acidity)
The Gratinée Topping
- 1 loaf French Baguette or Sourdough (cut into 1-inch thick slices)
- 2 cups Gruyère Cheese (freshly grated)
- 1/4 cup Parmigiano-Reggiano (finely grated for extra saltiness)
- 1 piece Garlic Clove (peeled, to rub on the toast)
👨🍳 Instructions
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1
In a heavy-bottomed Dutch oven or large pot, melt the butter with the olive oil over medium-low heat. This combination prevents the butter from burning during the long cook.
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2
Add the sliced onions to the pot and toss to coat thoroughly with the fat. Cover and cook for 15 minutes to allow them to sweat and soften.
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3
Remove the lid, increase heat slightly to medium, and stir in the salt and sugar. Cook the onions, stirring every 5-10 minutes, for 45-60 minutes. They should transform from translucent to a deep, jammy mahogany brown. If they stick too much, add a tablespoon of water to deglaze.
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4
Add the minced garlic and cook for 1-2 minutes until fragrant, being careful not to burn it.
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5
Sprinkle the flour over the caramelized onions and stir constantly for 2 minutes to cook out the raw flour taste.
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6
Pour in the dry sherry to deglaze the pot, scraping up all the brown bits (fond) from the bottom. This is where the concentrated flavor lives!
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7
Slowly whisk in the beef broth. Add the thyme bundle and the bay leaf. Bring the mixture to a simmer.
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8
Reduce heat to low and simmer uncovered for 30 minutes. This allows the flavors to meld and the broth to enrich.
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9
While the soup simmers, preheat your oven to 400°F (200°C). Arrange bread slices on a baking sheet and toast for 5 minutes per side until golden and crisp. Rub each slice with the raw garlic clove.
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10
Discard the thyme sprigs and bay leaf. Stir in the balsamic vinegar and season with additional salt and freshly cracked pepper to taste.
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11
Ladle the hot soup into oven-safe ramekins or crocks, leaving about half an inch of space at the top.
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12
Place one or two slices of toasted bread on top of the soup. Generously pile the grated Gruyère and Parmesan over the bread, ensuring the cheese reaches the edges of the bowl to create a seal.
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13
Place the crocks on a baking sheet and broil for 3-5 minutes, or until the cheese is melted, bubbly, and has developed dark brown spots.
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14
Let the soup rest for 2-3 minutes before serving—the crocks and the cheese will be incredibly hot!
💡 Chef's Tips
Don't rush the onions; the deep brown color is the only source of flavor for the soup, so give them the full hour if needed. Always grate your own cheese; pre-shredded cheeses are coated in potato starch which prevents that perfect, gooey melt. Use a high-quality beef bone broth or 'fond de veau' for a gelatinous, rich mouthfeel that water or cheap bouillon can't replicate. If the soup is too sweet from the onions, an extra splash of balsamic or a squeeze of lemon juice right at the end will balance it perfectly. Ensure your bread is toasted very hard; this prevents it from turning into complete mush the moment it hits the broth.
🍽️ Serving Suggestions
Pair with a crisp, acidic white wine like a French Chablis or a dry Riesling to cut through the richness of the cheese. Serve alongside a simple green salad with a sharp Dijon vinaigrette to provide a refreshing contrast. A glass of the same Sherry used in the cooking makes for an excellent aromatic accompaniment. For a full bistro experience, follow the soup with a light main course like Steak Tartare or Roasted Chicken.