First make the filling. Peel and cook potatoes. Mash the potatoes as you would normally, adding butter and milk.
Chop onion and you can either cook in some butter to soften and add it to the filling or you can add it to the sauce, your choice. I prefer it mixed in with the filling.
For the dough mix all ingredients to a pie crust consistency. Roll out dough to a thin 1/8 inch thickness. (not so thin it tears) Cut dough into circles using a coffee cup or like cup.
On half of the circle place approximately 2 tablespoons of filling. Fold over and seal with a fork around the edges. If it is too sticky sprinkle some water around the edges before sealing.
Place pierogies into a pot of boiling water. When they rise to the top they are done.
While pierogies are cooking. Place a stick or two of butter in a small sauce pan to melt.
When peirogies are done serve with melted butter on top. Salt and pepper to taste.
You can also boil, deep fry (until golden), or pan fry with butter/margarine and onions. You can also vary the fillings to your liking by adding other types of cheeses, bacon, sauerkraut, sour cream, etc.