Divide the dough into 2 equal portions and keep the other half covered until you're ready to use.
Lightly flour a work surface and roll out the first half of dough to 1/8" thickness and use a 3" circle cutter to cut out rounds.
Spoon about a tablespoon of filling onto the middle of it. Fold the dough in half to enclose the filling, bringing the edges together to form a crescent shape. Pinch the two sides together at the top, then work your way down on both sides, pinching the dough over the filling and pushing in the filling as needed, making sure the potato mixture does not break the seal. Place the finished pierogies on a baking sheet lightly dusted with flour.
Repeat with the second piece of dough. You can gather up any scraps and bring them back together to roll out a few more, or save the scraps to boil as a rustic pasta. Repeat the process to fill all the pierogies. At this point, you can cook all the pierogies or freeze them, or just freeze a portion.