Prepare pastry; rollout 1/4 inch thick. Cut to fit the tops of six individual casseroles. Bake on ungreased baking sheet at 450 degrees fro 10 to 12 minutes. Meanwhile, cook onion in butter until tender but not brown. Blend in flour and salt. Cook, stirring constantly until flour is cooked. Add broth all at one time. Cook and stir until thick and bubbly; add remaining ingredients. Heat till bubbling. Pour into 6 heated individual casseroles. Place pastry on hot filling just before serving. Serves 6. Note: If you want to be incredibly daring (for the 1950s), add 1/2 cup chopped mushrooms and a tablespoon of sherry!