Pierogi with sauerkraut and mushrooms

Ingredients (dough): 3 cups of all-purpose flour, 1 tsp of salt, about 1 cup of hot water
Ingredients (filling): 1 kg of sauerkraut, about 10 big mushrooms (dried or fresh; I live in Japan, so I use shiitake mushrooms), 1 big or 2 medium-sized onions, salt and pepper
Prepare the filling: strain the sauerkraut really well, then press it so that you squeeze out the liquid. (I just squeeze it with my hands.) Chop the sauerkraut finely and set aside. Chop the onions and the mushrooms. Fry the onions and in a large skillet or a wok, add the mushrooms and fry some more. Add the chopped sauerkraut, salt and pepper, mix well and cook on a small fire, stirring occasionally, until all the liquid is gone. Set aside and let it cool.
Prepare the dough: add the flour and salt to a large bowl, whisk to combine, then add the water. IMPORTANT: THE WATER MUST BE HOT, about 80 degrees C (176 F). If it is difficult to mix at first, use a knife or a flat spoon to mix. Knead the dough so that it’s smooth and not sticky. A lot depends on the flour, so you might add more water or more flour eventually; don’t worry! Just make it so that it’s elastic and doesn’t stick to your fingers. Put it aside in a bowl, covered with a clean linen cloth, for 30 minutes.
Make the pierogi: roll the dough, not too thinly, on a flat surface lightly dusted with flour, and cut the little disks with a mug cup or whatever you like. (I don’t recommend a glass, if you have a firm grip, because I crushed the glass in my hand when I was making my first pierogi hehe! and I’m not strong at all.) The disks should be large enough to allow you to put about one tsp of filling inside. Fold the dough in half and close by pinching the edges together.
Cook the pierogi: in a large pot, bring water to a boil, then add about 6-10 pierogi to the pot, stir to prevent them sticking to the bottom of the pot, and wait until they rise to the surface, then boil a little more and finally take them out to a colander or whatever you have to drain, rinse and repeat until all pierogi are done.
Eat the pierogi: straight after cooking, with vegan butter or fried onions. Or you can fry them, if you like. I usually eat them boiled on the first day, and then fried.
That’s it! I’m sorry for the length. I know it looks difficult at first, but if you love pierogi, you can try making them as often as you like, and eventually it will get really easy. I’ve been craving pierogi for so long, my New Year resolution was to learn how to make them well Good luck! Please let me know if there are any unclear points.