You can freeze the cheese piroshki two ways. They can be frozen before cooking as well as after cooking. To freeze raw, simply prepare up to the point of cooking. Lay on a lined baking sheet and freeze for 2 hours until the dough has hardened. Then, place them into a dated and labeled bag or airtight container, adding a layer of parchment or waxed paper between each piroshki. The second method is to freeze after they have been fried. Just allow the cheese piroshki to cool completely before stacking with parchment or waxed paper between each piece. Add to a dated and labeled bag or airtight container. They are good for 2 months in the freezer. To reheat already cooked piroshki, thaw overnight and quickly heat in the oven or pan. To cook raw piroshki from frozen, it is best to thaw before cooking. If you want to cook from frozen, do so in the oven at 400°F for 20 minutes.