Bennigan's Onion Soup

1/2 pound Firm white onions sliced
1/4 cup Butter
2 tablespoons Corn oil
3 tablespoons Flour
1 quart Chicken broth
1 quart Beef broth
8 slices French bread
Swiss cheese shredded
Parmesan grated

Saute onions in butter and oil until onions are transparent, but not well browned. When tender, turn heat to lowest point and sprinkle with flour, stirring vigorously. Pour into Dutch oven and stir in broths. Heat thoroughly and divide among 8 oven-proof bowls. Mix equal parts of cheese to smooth paste and spread over bread. Float a slice of bread atop each serving. Place all bowls on oven rack 4" from broiler heat and broil until cheese melts. Serve at once. Leftover soup freezes well up to 6 months.