Classic Polish Potato Pierogi

Method

1. In a bowl, mix flour, egg, water, and salt to form a dough. Knead until smooth, then let rest for 30 minutes.
2. Boil potatoes until tender, mash them, and mix with sautéed onions and butter.
3. Roll out the dough, cut into circles, fill with potato mixture, and fold into half-moons.
4. Boil the pierogi in salted water until they float, then drain.
5. Serve with sour cream and fried onions on top.