Combine all the ingredients for the butter sheet together and flatten the mass between 2 pieces of parchment paper until it's slightly smaller than your casserole dish. Then freeze the butter sheet for about 30 minutes.
Preheat the oven to 325°F. Peel all of the potatoes and cut the ends off of 9 of them. Using a peeler, cut the 9 potatoes without ends into 1½-inch thick ribbons. Boil the whole potatoes, potato ends, and the potato ribbons in salted water.
Roll up the potato ribbons (secure them with toothpicks if necessary), place them in water, and set aside for later.
Combine the meatball ingredients and form 25 mini meatballs from the ground beef mixture.
Add the whole potatoes and potato ends to the casserole dish and mash them. Place the meatballs on top of the mashed potatoes.
Take the potato ribbons out of the water and let them drain or pat them dry before placing them on top of the meatballs.
Take the butter sheet out of the freezer, remove the parchment paper, and place it on top of the potato ribbons.
Bake the potato casserole at 325°F for 35 minutes.
