In advance cook potatoes in water with 34 teaspoon salt Drain cool 10 minutes
Peel potatoes and slice
Pour Italian dressing over potatoes and refrigerate for at least 2 hours Remove egg yolks from egg and set aside
Chop whites
Mix egg whites celery and 1 cup green onions with potatoes and set aside Press egg yolks through sieve reserving 3 tablespoons for garnish Combine remaining egg yolk mayo sour cream mustard salt horseradish celery seed and pepper in bowl
Mix with potatoes Cover and refrigerate 2 hours before serving