Preheat oven to 400°. For soup, slice onions on slicer. Melt butter over medium heat in 6-qt dutch oven; add onions and sugar. Saute 15-18 minutes, stirring frequently until very tender and golden brown.

Stir in flour and salt. Gradually add beef broth and wine; bring to a boil over medium-high heat stirring constantly.

Add salt and pepper to taste. Cover and simmer over low heat 10 minutes.

For Croutons: place bread slices on a baking sheet and bake for 5 minutes. Turn bread over and sprinkle with cheese; continue to bake 5-8 minutes.

Ladle soup into bowls and top with crouton.