Our family has made this baked mashed potato dish every holiday since like 1994. It's a modified version of a recipe my mom found in the Delaware News Journal around then. It can be made ahead of time (up to two days), and then baked day of. Best served hot out of the oven though. This is the full fat / butter version of what was originally a "light / low fat / margarine" recipe, which was the style at the time.