Sauerkraut filling is one of the quintessential flavors for stuffing polish pierogi and polish naleniki, also known as blintzes or crepes. Since these are meatless, they would be perfect for meatless lenten meals or for wigilia, also known as christmas eve supper. The sauerkraut filling can be made one day ahead of time and refrigerated until ready to use. Then you can make the dough, roll, and fill it. You can enjoy the pierogi after they have been boiled. Or, take it a further step and fry them in butter with some onions.