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Ingredients
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Soup
Gratinée / Topping
Optional Garnish
Method
Soup
- 1
- 2
Caramelize onions
In a large heavy-bottomed pot or Dutch oven, heat 1 tablespoon olive oil and 3 tablespoons unsalted butter over medium heat until butter melts and foams. Add the sliced onions in an even layer. Sprinkle 1 teaspoon sugar and 1 teaspoon salt over the onions. Cook, stirring every 3–5 minutes, reducing heat if they’re browning too quickly. Continue for 30–40 minutes until the onions are deep golden brown and sweetly caramelized. If onions stick, deglaze periodically with a tablespoon of water and scrape browned bits from the bottom.
- 3
Add flour and deglaze
Raise heat to medium-high, sprinkle 1 tablespoon all-purpose flour over the onions and stir for 1–2 minutes to cook the raw flour taste. Pour in 1 cup dry white wine (or sherry) to deglaze, scraping up browned fond from the bottom. Let the wine simmer and reduce by half, about 2–3 minutes.
- 4
Simmer soup
Add 6 cups beef stock, 1 bay leaf, 2 thyme sprigs, and 1 teaspoon Worcestershire sauce. Bring to a simmer, then reduce heat to low and simmer gently uncovered for 20–25 minutes to meld flavors. Taste and adjust seasoning with additional salt and freshly ground black pepper (about 1 teaspoon total or to taste). Remove and discard the bay leaf and thyme sprigs before serving.
Gratinée / Topping
- 5
Toast the baguette slices
Preheat oven to 375°F (190°C). Brush both sides of the baguette slices lightly with 2 teaspoons olive oil or melted butter and place them on a baking sheet. Toast in the oven until lightly golden and crisp, 6–8 minutes, flipping once. Remove and set aside.
- 6
Assemble for broiling
Ladle the hot soup into ovenproof bowls or crocks, filling each about three-quarters full. Place one or two toasted baguette slices on top of each bowl of soup (they will float). Generously mound about 1/4 cup grated gruyère on each bowl (totaling roughly 2 cups for 8 servings) and sprinkle a little of the 1 tablespoon finely grated parmesan over the gruyère to aid browning.
- 7
Broil until golden
Preheat the oven broiler on high with the rack about 6 inches from the heat. Place the prepared bowls on a baking sheet to catch any spills and broil until the cheese is bubbly and deeply golden brown in spots, 2–5 minutes. Watch carefully to avoid burning. Remove from oven using potholders.
- 8
Finish and serve
Sprinkle optional fresh thyme leaves and a crack of black pepper over each bowl if desired. Allow to rest 1–2 minutes (cheese will be very hot) and serve immediately.