Melt in double boiler 1 tablespoon butter. Stir in and melt 1 1/2 cups diced Velveeta cheese. Add:

1/3 tsp. salt
1/4 tsp. dry mustard
1 tsp. Worcestershire sauce

Stir in slowly 1/2-3/4 cup light cream. When mixture is hot, remove the pan from heat. Beat in 1 egg yolk. Serve at once over toast points or crackers.