As a result, this weekend I made homemade pierogies.
I started by peeling (& boiling) enough potatoes to make about 2 or 3 cups of mashed potatoes.
While they were cooking, I made the dough:
You beat 2 eggs with 1/2 cup of oil until they're light in colour, then add 1.5 cups warm water and 1.5 tbsp salt. Next, you gradually add 5 cups flour and knead until it's a soft dough. (I started by using the mixer, but finished kneading it by hand.) Cover the dough, and let it rest for 10 minutes.
Luckily, while the dough is resting, you can grate the cheese. When the potatoes are soft, mash them, then add the grated cheese. Let it melt, then mix. Let them cool a bit so they don't burn your hands during the next step.
Next, stop eating the cheesy mashed potatoes. You can eat the leftovers later.
Roll out the dough, then cut in diamonds. (The recipe says to cut with a round cookie cutter, but I'm too lazy for that - diamonds work just as well, you just end up with triangles instead of half circles.
Put a scoop of the potato mixture on each diamond, then fold into triangles and seal the edges.
Put them in a container separated by waxed paper, and freeze (if you don't plan to eat them immediately).
To cook, boil a pot of salted water, drop the pierogies in and stir. Let them boil for about 10 minutes, then strain. (You want to let them cook several minutes after they float to the top.) After that, you can fry them in butter & onions if you want.