Freezing pierogi is quite easy.
You start by being sure that when you boil the pierogi you have a slight amount of oil on the water. The oil will form a film on top of the water and when you remove your pierogi it will cover them. This will prevent them from sticking together.
You do this whether you are going to freeze the pierogi or serve them immediately.
Shorten the boiling time for pierogi that you intend to freeze to about two minutes from the time the water starts to boil after you have put the last pierogi in the pot.
It is best to use a large pot to boil the pierogi so that you don’t chill the water too much and over cook the pierogi while the water is coming back to the boiling point.
Remove the pierogi and put them on a drying rack or baking sheet and allow them to dry enough that the water is no longer on the surface of the pierogi.
When dry, put them on a plastic cutting board or a baking sheet on which there is baking paper. Put the pierogi side-by-side and do not allow them to overlap. They can touch each other but they should not overlap.
Put the baking sheet or cutting board in your freezer for 15 to 20 minutes to allow the surface of the pierogi to get hard. You can leave them longer but that is not necessary because all that you are trying to do is get the surface hard.
In the wintertime you can put the baking sheet or cutting board on your balcony and allow them to freeze outside.
Once the pierogi surfaces are hard, remove them from the baking sheets and pack them in a container or plastic bag. Be sure that the packing is airtight so the pierogi do not dry out.
Put the container back into the freezer and allow the pierogi dough to completely freeze.
To serve, put them in boiling water. The water will chill. When it starts to boil again, take them out immediately.