Celery Seed Potato Salad

6  med  Red or Yukon Gold potatoes, unpeeled
4  hard cooked eggs, diced
2  celery ribs, finely chopped
1  small onion, finely chopped
1  tsp  salt
1  tsp  celery seed
6  Tbs  sugar
1/2  tsp  cornstarch
1/2  tsp  ground mustard
1/4  cup  heavy whipping cream
1  egg, well beaten
2  Tbs  white vinegar
1/2  cup  mayonnaise
1-1/2  Tbs  butter

Place potatoes in large pot; cover with water. Bring to a full boil. Reduce heat; cover and simmer for 20-25 minutes, or until just fork tender. Drain. When cool enough to handle, peel and cube. Place in a large bowl. Add hard-boiled eggs, celery, onion, salt, and celery seed. Set aside.

In small saucepan, combine sugar, cornstarch, and mustard. Stir in cream, egg, and vinegar until smooth. Cook and stir over medium heat until mixture coats the back of a metal spoon. Cook and stir 1-2 minutes longer, or until thickened. Remove from heat; let stand for 20 minutes.

Whisk in mayonnaise and butter until smooth. Cool slightly. Pour over potato mixture; mix well. Cover and chill at least 6 hours.