In a Dutch oven or other large pot, melt 3 Tbsp. unsalted butter on the stovetop over medium heat. Add 1 Tbsp. vegetable oil and 3 lbs. Vidalia onions (about 4 medium), halved lengthwise, peeled, and thinly sliced, and cook until onions are softened, stirring occasionally, about 15 minutes. Add 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt, ½ tsp. freshly ground black pepper, and ½ tsp. granulated sugar. Continue to cook, stirring occasionally, until onions are deep brown, almost mahogany in color, and caramelized, reducing heat slightly if onions seem to be browning too quickly, 45 minutes to 1 hour more. (If the bottom of your pot begins to burn at any time during the cooking process, add 1–2 Tbsp. water and scrape the bottom, stirring in the browned bits.) Do ahead: Caramelized onions can be prepared 1 week ahead; refrigerate in an airtight container or freeze for up to 6 months.

Add 1½ cups dry white wine such as sauvignon blanc or pinot grigio and raise heat to high. Cook until almost all liquid has evaporated, 8–10 minutes.

Tie 10 sprigs fresh thyme and 2 dried bay leaves into a bundle with twine. Add 6 cups Beef Bone Broth or store-bought low-sodium beef stock and herb bundle to pot with onions. Bring to a boil, reduce to a simmer, and cook, uncovered, until broth is thickened and flavorful, 20–30 minutes. Remove from heat and whisk in remaining 2 Tbsp. unsalted butter. Taste and adjust seasoning with additional kosher salt and freshly ground black pepper. Do ahead: Soup can be made 3 days ahead; refrigerate in an airtight container or freeze for up to 6 months. Reheat over medium until steaming.

To serve, position a rack in the upper third of the oven and heat the broiler to high. Cut two ½-inch baguette slices for every serving of soup. Place baguette slices on a rimmed baking sheet and toast in oven until crisp and dry but not browned, about 1 minute per side. Rub one side of each toast with the 1 garlic clove, cut in half lengthwise, and set aside.

Place ramekins, crocks, or ovensafe bowls on a rimmed baking sheet, add ½ tsp. sherry, preferably Fino or Manzanilla, to the bottom of each, and ladle soup on top. Top each serving of soup with two garlic-rubbed toasts. Divide 4 oz. (about 1 cup) coarsely grated Gruyère cheese among the servings, covering the toasted bread slices and some of the soup. Carefully transfer baking sheet to oven and broil until cheese is melted and bubbling, 4–8 minutes. (Alternatively, if using regular soup bowls: Top each garlic-rubbed toast with some cheese and return to broiler to melt, about 2 minutes more. Divide sherry and soup among bowls, sprinkle with remaining cheese, and top each serving with two cheese toasts.) Editor’s note: This French onion soup recipe was first printed in February 2015; it has been updated to lengthen the cooking time for the onions. Head this way for more of our favorite soup recipes →