4 c. sliced, boiled potatoes (1 1/2 lb.)
1 med. onion (thinly sliced)
2 tsp. sugar
1/2 tsp. salt
1/2 tsp. wet mustard
1/8 tsp. pepper
1/4 c. vinegar
1/4 c. water
1 tbsp. soft butter
1 tbsp. flour
1 egg

Combine potatoes and onion. Combine sugar, salt, mustard, vinegar, and water in small saucepan. Blend together butter and flour, add slowly to liquid, stirring. Cook five minutes. Whisk hot mixture slowly into egg. Pour hot dressing over potatoes and toss lightly. Garnish with parsley.