Preheat oven to 375 degrees F (190 degrees C).

Melt the butter in a large skillet over medium high heat. Place the onion in the butter and saute for 5 to 10 minutes, or until tender. Stir in the thyme and remove from heat.

In a large pot over high heat, combine the consomme, bay leaves and white wine, if desired. Bring to a boil, reduce heat to low, stir in the sauteed onions and allow to heat through, about 10 to 15 minutes.

Ladle soup into 4 individual oven-safe bowls, filling each about 3/4 of the way. Top each bowl with 2 slices of baguette bread and then cover each with the cheese.

Bake at 375 degrees F (190 degrees C) for 10 to 15 minutes, or until cheese is melted and bubbly.