Polish Pierogi with Potatoes and Cheese

Method

1. In a bowl, mix flour and salt
2. Add egg and cold water, knead until smooth
3. Cover and let rest for 30 minutes
4. Boil potatoes until tender, mash with cheese and milk
5. Divide dough into small balls, flatten into discs
6. Place filling in the center, fold, and seal
7. Boil until they float, then fry in butter