Preheat the broiler. Combine the butter and cheese in the top of a double boiler over simmering (not boiling) water. Cook, stirring constantly, until the cheese melts. Stir in the ale and cook until smooth and mixed. Remove the pan from the heat and stir in the Worcestershire sauce, mustard, cayenne, and salt. Place pieces of toasted bread on a heat-proof plate or baking sheet. Top with the sauce. Place the bread under the broiler until bubbly. Serve hot.