1/2 c. white sugar
1 heaping tbsp. flour
1 c. milk
2 egg yolks
1 tbsp. mustard
1/2 tsp. salt
1/2 c. vinegar

Put all ingredients except vinegar in a small saucepan; mix well and bring to a boil. Add vinegar, stirring constantly. Put in piece of butter the size of a walnut. Boil until thick. To serve, cut boiled eggs in half and pour sauce over them.