1/3 c. sugar
1 1/2 tbsp. cornstarch
1 tsp. dried mustard
1/2 tsp. salt
1/4 c. vinegar
1 egg
1/4 c. water
1 c. mayonnaise

Mix sugar, cornstarch, mustard and salt in saucepan. Add water, vinegar, and egg; cook mixture over low heat, stirring occasionally until it thickens. Remove from heat.

Let cool; add mayonnaise.

This is very good in potato salad; refrigerated overnight.