French Onion Soup

¼ cup butter
½ cup cooking sherry
2 large onions (thinly sliced like onion rings)
2 cans beef broth
1 loaf French bread
1 tsp sugar
Sliced swiss cheese
1 tbls flour

Melt butter in a large saucepan. Add the sugar (for caramelizing) and onions and cook till golden-brown (about 20 min.). Toss in flour and stir. Add sherry and beef broth and bring to a boil. Preheat oven to 425 degrees. Reduce heat of stove to low and simmer soup, covered, for 10 minutes. Ladle soup into oven-safe bowels, add toasted bread and cheese slices on top, and bake on a cookie sheet in oven for 10 minutes.