Pierogies are little pockets of dough filled with any number of things. We use mashed potatoes and cheese, for a savory side dish great with any meal.
Peel and slice or chop potatoes. Put in cold water and set on the stove to boil. It helps to rinse them with water a couple times before cooking to remove some of the starch.
Once fork tender, drain well.
Mash or whip the potatoes, just as you would make any mashed potatoes. Add butter and milk & mash or whip well, to create lump free potatoes.
Stir in the grated cheese (or sauerkraut, or onions, mushrooms, etc). Cheese will melt into hot potatoes.
Allow to cool.
Place all the flour in a bowl, and add all the eggs and salt at once. Use the dough hook of a mixer to mix well and knead for several minutes. If it's too dry, add a tbsp of water. This can also be done my hand on a floured board. Even with the mixer, I usually turn out and knead a few time by hand. wrap in plastic and let rest once done.
Roll out the dough about 1/8th of an inch thick - fairly thin since it will puff a bit once cooked. Cut into rounds, about 3" in diameter. A cookie cutter works, or even a glass or clean open ended can.
Place 2-3 tsp of cold mashed potato mix on one half, fold over into a half moon, and seal the dough with a bit of water. Make sure the edges are pinched closed, otherwise the filling will disappear into the boiling water when being cooked. The dough is quite flexible and will stretch to cover the filling.
Place the filled pieces on cookie trays, and cover with a towel until ready to cook. I prefer to freeze them at this point, but you can also continue on, below, and then freeze.
Heat a large pot of water. Once it simmers well, or comes to a low boil, drop the pierogies in a few at a time. Stir to make sure they done't stick to the bottom. They will float to the surface as they cook, about 5 minutes. I flip them over for a couple minutes before removing them with a slotted spoon or spider, allowing all water to drain off.
Drop into a well butter bowl. My mother-in-law melted butter ( a lot of butter) and kept it warm to pour over them. The butter prevents them from sticking together.
At this point, the pierogies can be eaten as is, although we prefer to fry them briefly in butter or olive oil. This is also where they can be frozen.
To freeze: lay them out on a parchment covered sheet pan, or use a silicon sheet. Leave them separated, and put the whole tray in the freezer to flash freeze. In an hour or so, once partially frozen, they can be removed and placed in zipper bags or vacuum sealed. Now I can remove as many as I want for a meal in the future. I usually put a dozen in a packet - enough for one meal for us.
Re-roll the dough as needed to use up the scraps once the rounds are cut. Do keep the dough covered as you work, otherwise it can dry out quickly.
Once the sheets of dough start getting longer, I cut in half or thirds and work one piece at a time.
When using a pasta maker, roll the dough to #5 or 6, and it will be just the right thickness.