Melt butter in large saucepan over medium-high heat. Add onions and cook 5 minutes or until golden brown, stiring occasionally. Stir in broth, wine and 1 cup water; heat to a boil. Reduce heat; simmer 10 minutes.
Divide soup between 4 ovenproof bowls. Top with bread and cheese. Place bowls under preheated broiler 5 inches from heat; broil 2 minutes or until cheese is melted.