French Onion Soup

Name: French Onion Soup
Ingredients: ¼ cup extra-virgin olive oil; 3 pounds sweet onions, such as Vidalia, halved and thinly sliced (9 cups); 2 tablespoons unsalted butter; 1 clove garlic, minced (1 teaspoon); 3 thyme sprigs; 1 bay leaf; Kosher salt and freshly ground white pepper; ½ cup dry vermouth or dry white wine; 2 quarts beef stock, preferably homemade; ⅓ cup sweet Marsala, Madeira, or port wine; 6 slices French bread or other soft country loaf (each 1 inch thick), lightly toasted; 8 ounces Gruyère, coarsely grated (2 cups)