1/4 c. vinegar
1 tsp. salt
2 tbsp. sugar
1 egg, beaten
1/2 tsp. prepared mustard
1 tbsp. butter

Mix vinegar, 1/2 cup water, salt, sugar and egg and mustard together. Place butter in small saucepan; melt over low heat. Add vinegar mixture; cook until thickened, stirring constantly. Cool.