Heat broiler. Melt butter in 5-quart saucepan over medium-high heat. Add onions; stir to coat with butter. Cover; cook 8 minutes, stirring occasionally. Add sugar; cook, uncovered, stirring onions until slightly golden, about 6 minutes. Add flour; cook 1 minute longer. Stir in beef broth, 1 broth can of water and the red wine. Simmer, covered, 5 minutes.
Place four 2-cup ovenproof bowls on a baking sheet. Put 1/3 cup croutons in each bowl. Evenly divide soup over croutons in each bowl (about 1-3/4 cups each). Top each with slice of cheese. Broil 3 minutes or until cheese is melted. Makes 4 servings.
