prep: 15 minutes
cook: 1 hour
cool: none
8 tablespoons (1 stick) unsalted butter
8 cups sliced yellow onion (about 3 medium)
2 garlic cloves, minced
4 thyme sprigs
2 bay leaves
¼ cup sherry (or white wine vinegar or additional broth)
6 cups (1½ quarts) beef broth
½ teaspoon kosher salt
¼ teaspoon freshly ground black pepper
8 to 16 crostini, homemade or store-bought
8 ounces Gruyère cheese, shredded (about 2 cups)
1. In a large soup pot, melt the butter over medium-high heat. Add the onion and sauté, stirring occasionally, until it begins to caramelize, 20 to 25 minutes. Add the garlic, thyme, and bay leaves and cook until fragrant, 2 to 3 minutes. Add the sherry and stir to loosen any browned bits on the bottom of the pot. Let simmer until almost all the liquid has evaporated, 1 to 2 minutes. Add the broth, bring the mixture to a low boil, and boil for 2 to 3 minutes. Reduce the heat to medium-low, stir in the salt and pepper, and simmer for 15 to 20 minutes to meld the flavors.
2. Position a rack 4 to 5 inches from the heat and turn the broiler to low if possible. (If a low setting is not available, then position the rack 6 to 8 inches from the heat.)
3. Discard the bay leaves. Ladle the soup into eight 12-ounce ovenproof bowls and place them on a sheet pan. Top each bowl with a crostini or two and cover with the shredded Gruyère.
4. Broil until the Gruyère begins to bubble and brown, about 5 minutes. Watch carefully; the cheese can burn quickly.
5. Serve immediately.
Makes 8 servings