In a skillet over medium heat add the butter. olive oil, and wine.
Once the butter is melted add the onion and mushrooms.
Sautee until the mushrooms are tender and caramelized.
Cut 6 to 8 slices of French bread. Butter both sides.
Bake in an oven that is set at 350 degrees F until golden brown on both sides.
Top the toast with mozzarella cheese and set back in the oven until melted.
Top with mushrooms and additional cheese if desired.
Serve while hot.