In a saucepan, cook onions in butter for 20 minutes. Stir in broth, water, Worcestershire sauce, and pepper. Bring to boiling.
Place French bread on a baking sheet. Broil 3 to 4 inches from the heat for 1 to 2 minutes per side or until toasted. Sprinkle with cheese. Broil for 1 minute more.
Top each serving with a slice of cheese-topped toast. Makes 6 side-dish servings.