1/4 c. butter
4 c. thinly sliced onion
4 (10 1/2 oz.) cans condensed beef broth, undiluted
4-6 slices French bread, 1 inch thick
1/4 c. grated Gruyere cheese
2 tbsp. grated Parmesan cheese

Melt butter in large skillet, saute onion until golden but not browned, about 8 minutes. In medium saucepan, combine beef broth and sauteed onion; bring to boiling. Reduce heat; simmer, covered, 30 minutes. Meanwhile, in broiler, toast French bread on both sides. Sprinkle each slice with grated cheeses, dividing evenly.

Broil just until cheese is bubbly, about 1 minute. Pour into bowls. Float toast on top, cheese side up. Flavor is enhanced if soup is refrigerated, covered, overnight, and reheated at serving time. 4-6 servings.