1/4 c. water
1/4 c. vinegar
1 egg
1 tbsp. mustard
1/2 c. milk
1/2 c. sugar
1 tsp. salt
1 tbsp. flour
1/4 c. mayonnaise
1 tbsp. butter

Boil water and vinegar. Take off heat. Mix together egg, mustard, milk, sugar, salt and flour. Pour into water and vinegar mixture, stirring constantly, over medium heat until thick. Remove from heat and add butter; when cool, add mayonnaise. Pour over macaroni or potatoes. Will keep up to 2 weeks in refrigerator.