The recipe is rather approximate, as such things tend to be.
2 cups flour
1 cup water
pinch of salt
1 cup kasza
a bunch of dried mushrooms (I used the gourmet blend from Costco)
5+ strips of bacon?
(I actually made a vegetarian version as well, so you might want to halve the kasza?)
Step one, which is probably best done a few hours in advance? is to rehydrate the mushrooms in warm water.
Then, bring 2 cups mushroom water to a boil (adding regular water if needed to make 2 cups) with salt and pepper. Add the kasza, stir, cover, and reduce heat to low. Simmer for 10 minutes, fluff, and set aside.
As its cooking, chop the bacon (finer is better) and fry it in a large, deep pan. As it fries, chop the onion, and once the bacon is browned, add it to the pan. Then chop the mushrooms (squeeze out the excess water, but don't worry about it too much) and add them to the pan. Saute for 5 minutes or so? Or until the flavors combine, then add the cooked kasza and stir. Let it cook a minute or two to combine the flavors, adding salt and pepper to taste. Set aside.
Now, the dough. According to what I've read, you want to use hot - even boiling - water. Add it to the flour and salt (you want a decent amount of salt here - I think I used too little), stirring with a wooden spoon. Then knead it with your hands (let it cool if need be) until it forms an elastic dough. Cover your "work surface" (ie clean table) with some flour, grab a hunk of dough and roll it out. You want it about 2mm thick - thin, but not so thin that it becomes porous or breaks. Use a glass to cut out circles, put a spoonful of filling in the center (you always need less than you think) and pinch shut.
This is the most labor intensive part of the process. I underestimated just how much work it involved. By the end, it had turned into an 8 person operation (though I made a seriously ridiculous amount of pierogi, with several other fillings too).
When you're about halfway through or so, set a large pot of water to boil with plenty of salt. Once it's boiling, drop in about 6 pierogi at a time, or however many the pot seems to hold comfortably (there should be room for them to form a single layer, with some space). Boil 2-3 minutes, or until they float to the surface.
Garnish with fried bacon and onions, and enjoy!
(We also did a potato and cheese filling, which just involved boiling some potatoes and mashing them with grated cheddar, salt, and pepper. I might have to try doing those again with some bacon bits folded in...)