The secret to this bistro favorite is the long, slow cooking of onions to allow their natural sugars to caramelize. Use aged Gruyère to get the traditional bubbling crust of cheese; it's smooth and melts easily.

Classic French Onion Soup

In a stockpot, heat butter and olive oil over medium-high heat until butter is melted. Add onions; cook for 15 minutes or until onions begin to brown, stirring occasionally. Reduce heat to medium-low; cook, covered, for 25 minutes more or until onions are golden brown, stirring occasionally.

Add sherry to stockpot. Cook over high heat until sherry evaporates, stirring constantly. Stir in beef stock and thyme. Bring mixture to boiling; reduce heat. Simmer, covered, for 20 minutes. Season to taste with salt and pepper.

Meanwhile for baguette toasts, preheat oven to 350 degrees. Grease a baking sheet. Arrange baguette slices on a baking sheet in a single layer. Bake for 15 to 20 minutes or until bread is crisp and lightly browned, turning once. Cool bread on a wire rack.

Position a rack 6 inches from the broiler and preheat broiler. Place 6 broiler-proof soup bowls or crocks on a baking sheet. Place 2 toasted baguettes in each bowl and ladle the hot soup on top. Sprinkle with cheese. Place baking sheet with bowls under the broiler and broil for 2 to 5 minutes or until the tops are browned and bubbly. Serve immediately.