Pierogies with potato,cheese and onion filling

When my son Kris was home from college a few weeks ago for Spring break he reminded me I hadn't made him pierogies in a while. I took that as Mom...how about it?? So today was pierogie day. It's a bit labor intensive but, hey, he's worth it and I, of course, had to sample a few for dinner, right? Mom has to eat, too!
So I got out my favorite recipe and proceeded to measure,stir,roll and stuff the little pot stickers, as they are also sometimes called.

This recipe is very good. The dough is made with lots of sour cream, I'm thinking that's an authentic Polish ingredient to add to the dough? How many this recipe makes depends on the size you make. I make mine kind of large and it makes about 3 dozen.

RECIPE FOR PIEROGIES WITH POTATO,CHEESE AND ONION FILLING

4 1/2 cups A.P. flour
2 tsp. salt
2 tbsp. butter - melted
2 cups sour cream
2 eggs
1 egg yolk
2 tbsp. veg. oil

6-7 med. potatoes - peeled and cubed
1 1/2 cups shredded cheddar cheese
salt & pepper

TO MAKE DOUGH:

In a large bowl, stir flour and salt. Set aside.
In a separate bowl,whisk butter,sour cream,eggs,yolk and oil.
Stir the wet ingredients into the flour/salt mixture til well blended.( Don't worry if it seems a little lumpy. It rolls out smooth).
Cover bowl with towel and let it rest about 20 minutes.

FILLING:

Cook potatoes til tender. Drain and mash with cheese. Season with salt & pepper.
Set aside to cool.
Separate dough into 2 balls. I usually divide again to work with smaller portions of dough.
Roll out to about 1/8" thickness and cut out circles. (I just use a glass. The size is up to you. My glass is about 3 1/2" in diam.)
After you have all the circles cut out you can roll them individually to get them even thinner. Place about 1 tbsp. of filling on one side and fold dough over so edges meet. With a fork dipped in flour, press the edges to seal. Trim away any excess dough if there seems to be too much and repress with fork.

Place pierogies in a single layer on a cookie sheet covered with waxed paper and put into freezer til frozen. Transfer when frozen hard to zip lock bags.
When you want to use, just put frozen pierogies into pot with lots of boiling water and gently boil til they float. Then fry in pan with butter.
We like them with sauted onions and more sour cream.( Ran out of sour cream for the photo...darn!).