I have experimented with this dressing, it is just so good. Instead of potatoes I used egg noodles. I have omitted the onions and made it like a noodle pudding with noodles and fruit cocktail. Have fun with it.
Boil new potatoes in skins, drain off water and set aside. Saute onions in butter until transparent and golden. Add sugar, salt and flour to onions. Heat stirring constantly. Slowly add in milk while stirring and cook until thickened. Add in sour cream and vinegar. Bring just to a boil and remove from heat. Pour mixture over cooked potatoes and stir until well blended.