French Onion Soup

Name: French Onion Soup
Ingredients: 5 tablespoons unsalted butter, divided; 3 pounds Vidalia onions (about 4 medium), halved lengthwise, peeled, and thinly sliced; 1 tablespoon vegetable oil; 1 teaspoon kosher salt; 1/2 teaspoon freshly ground black pepper; 1/2 teaspoon granulated sugar; 1 1/2 cups Epicurious Chardonnay; 6 cups homemade beef broth or store-bought low-sodium beef broth; 10 sprigs thyme; 2 bay leaves; 1 baguette; 1 garlic clove, cut in half lengthwise; 2 teaspoons sherry; 4 ounces Gruyère cheese, grated (about 1 cup); kitchen twine