- For filling: Combine mashed potatoes, grated cheese, melted butter and 4 eggs.
- Separate remaining egg and put yolk into the filling, the white into a small bowl and set aside.
- Egg white is used to seal filling inside dough circles.
- For dough: Combine ingredients for dough, adding a sprinkling of water if necessary.
- Roll out dough, press out circles. (An empty soup can may be used to make circles out of the rolled dough.)
- Brush egg white all around inner edge of circles.
- Put 1 tablespoon filling in center; top with another circle and press with fork to seal edges together.
- Cooking: Put water into deep pot and bring to boil.
- Drop pierogi into water a few at a time.
- They will sink to the bottom and when they float to the surface, remove and drain.
- Repeat until all pierogi are cooked.
- In heavy skillet melt butter and add onions.
- Cook onion until transparent; add pierogi and fry golden.
- Serve hot with onion.
- To freeze: Dust with flour, put on cookie sheet and freeze.
- When ready to use, put frozen pierogi in boiling water and proceed as above.