Classic Polish Pierogi with Potatoes and Cheese

Method

1. In a large bowl, mix flour and salt.
2. Add milk, egg, and 1/2 cup water. Knead until smooth. Cover and let rest 30 minutes.
3. Boil potatoes until tender. Mash with cheese, sour cream, and a pinch of salt.
4. Roll out dough into thin sheets. Cut into circles. Fill with potato mixture.
5. Boil pierogi in salted water until they float. Drain.
6. Sauté onions in butter until golden. Serve with pierogi.