Once you get into a groove, these pierogi are really easy to make. Go ahead and make extra - they can be frozen for a quick weeknight meal. After forming the dumplings (don't boil), arrange them in a single layer on a baking sheet and freeze until solid, then transfer to a zip top bag for long-term storage. Cook them right from the freezer, just add a few extra minutes to the boiling time. Yields about 20 pierogi.