Perogies.

Filling:
2 cups shredded sharp cheddar
1 large cooking onion diced small
5 lbs red potatoes
1 tsp salt
3/4 cup butter

Sauté diced onions in butter until slightly caramelized.
Prepare potatoes like you would for mashed potatoes, drain.
Put hot potatoes into kitchen-aid bowl with the mixer blade and mash the potatoes.
Add the sautéed onions and butter, salt, and shredded cheese mix until the cheese is well blended with potatoes.  The only lumps should be small bits of onion.

Dough:
3 cups flour
1/2 teaspoon salt
1/4 cup sour cream
1 egg
1 cup water

Combine flour, salt, sour cream, egg, and water in a large bowl.  Mix until dough comes together. If dough is dry, add water, until it's moist and springy.  If the dough is sticky add more flour until it's smooth.

On a floured work surface, knead dough for 3 or 4 minutes until elastic.  Cover dough with plastic wrap and refrigerate for at least 30 minutes.
Roll dough out quite thin, 1/8" thick, using a round cutter cut as many 2-3" circles as you can from one rolling.  The more times it is rolled the tougher the dough gets.
Put one of the circles in your hand and spoon in a scoop of filling making sure not to get the edges where you will crimp it together.  If filling gets in the crimp edges they fall apart.  Fold the dough over the filling and crimp the edges closed leaving no gaps or the filling will escape when they are boiled.  Place on a floured surface so the dough doesn't tear when you pick them up.
Have someone put a large pot of water on to boil while you're crimping edges so you can boil them a batch at a time.  Boil them until they float then take them out and put them in a bowl with some melted butter so they don't stick together.  I usually put them on cookie sheets making sure they don't touch each other and cover it with saran wrap and freeze them.  Once they are frozen put them in large ziplock bags and take out only what you want to cook.
Once they are boiled and the dough is cooked they can be fried or eaten boiled. We usually fry them with bacon and caramelized onions.  some people put bacon right in the filling, We eat them with sour cream.