1. To make the soup, heat the butter and oil in a large stock pot. Add the onions and cook over hight heat, stirring occasionally, for 15 minutes. Add the garlic and sugar. Reduce heat to medium and cook, stirring occasionally, until the onions are golden brown, about 40 minutes.

2. Pour in the Cognac, warm it, and flame with a match. When the flames subside, add the mustard and thyme. Stir in the flour and cook, stirring frequently, for 3 minutes.

3. Gradually stir in the stock and wine. Season to taste with salt and pepper. Simmer uncovered over medium heat for 1 hour.

4. Preheat oven to 350 degrees F.

5. To make the croutons, spread one side of each bread slice with 1 1/2 teaspoons of butter and 1 1/2 teaspoons oil. Sprinkle with the garlic. Toast the prepared side only on a baking sheet until crusty and golden, 12 to 15 minutes.

6. Combine the 3 cheeses for the gratinee.

7 Preheat the broiler.

8. Ladle the hot soup into 8 oven-proof bowls to fill three-fourths full. Float a crouton in the center of each bowl. Top each bowl lavishly with the cheeses. Broil 6 inches from the heat until the cheese is melted and bubbling, about 4 to 5 minutes. Serve immediately