1 8 oz. cheddar cheese as mild or sharp as you prefer, coarsely grated
1 tbsp. unsalted butter
Salt to taste
1 tsp. Dijon-style mustard
Small pinch cayenne pepper
1/2 c. milk
1 egg, slightly beaten

In the top of a double boiler or in a heatproof dish fitted over a pot of simmering water, heat the cheese, butter, salt, mustard and cayenne, stirring occasionally, until the cheese melts. Add the milk and egg, and stir constantly until the mixture thickens. Taste and add more salt if desired. Pour over toast.