This traditional potato perogy filling is the very basic perogy (also called varenyky) that we all know and love. It is made plain (potato only) or with either cottage cheese or cheddar cheese (I use one or the other, but not both).and basic seasoning of salt and pepper and onions. If you are making a traditional basic recipe it usually always has cottage cheese in it. If you want a cheddar filling, then either omit the cottage cheese and substitute it with the same amount of grated cheddar cheese. The point is that they are very customizable, as long as…