Preheat oven to 350°F.

In large pot of salted boiling water, cook shells until done. Drain and let cool.

Put potatoes in a pot and cover with 2 inches of water. Bring to a boil and cook until potatoes are fork tender. Drain.

Return potatoes to the pot. Mash and add a tablespoon of butter, and all the cheese. Add salt and pepper to taste. Mix well and let cool.

Fry onions in butter until softened, and translucent. Set aside.

Spoon potato and cheese mixture into shells. Put in a large casserole or 9x13 baking pan.

Pour onions and butter mixture over shells.

Place in oven for a half an hour, or until heated through.

Can be served as main dish or with a nice salad, or with kielbasa, pork chops, or whatever you like to eat pierogies, with.

Enjoy!