1/2 cup white sugar
2 tablespoons all-purpose flour
1 teaspoon prepared mustard
1/2 teaspoon salt
1/4 cup white wine vinegar
1/4 cup water
1 egg, beaten
Whisk together the sugar, flour, mustard, salt, vinegar, water and egg.
Cook in a double boiler until thick; allow to cool. Mix with equal parts mayonnaise and stir into potato salad.