Pierogi are easy once you get the right combo of textures with your dough and fillings. Potato and cheese should be tight enough to roll into a ball and hold its shape (think drier than normal mashed potatoes). Cabbage should be allowed to chill in the fridge so the butter solidifies and holds it together as you scoop it out with a spoon. Ditto prune - once it’s cooled it should be similar to a nice, spreadable jam. Your dough should be just the tiniest bit elastic and allowed to rest for at least 30 minutes before laminating it with flour through the dough roller a couple times and then rolling it into sheets for cutting. A washed out 28 ounce can is the perfect size for cutting the dough, and you gotta make sure they’re sealed completely (dip a fingertip in water and run it along half the circle of dough) when you crimp them shut.

Source: helped to make literally hundreds of pierogi yesterday.