Bring a large pot of heavily salted water to a boil over high.
Line a baking sheet with parchment to lay finished pierogies. Lightly flour your work surface, then roll out the dough until 1/8-inch thick. Using a 3-inch cookie cutter punch 16-18 disks of dough.
Place 1 1/2 - 2 teaspoons of filling on each circle of dough. Gently fold the dough over, forming a pocket around the filling. Pinch the center edge of the dough together and 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. If needed use dap some water to help seal edges. At this point the pierogies can be frozen up to 4 weeks or refrigerated overnight.
Heat 12 inch skillet over medium heat and add 2 tablespoons of butter.
To cook the pierogi, add a single layer of pierogi to the pot of boiling water. No more than 10 at a time to prevent sticking. Cook until they rise to the surface, about 2 minutes, then cook another 2 to 3 minutes until puffy. Frozen pierogies may need an additional couple of minutes. Use a slotted spoon to drain and transfer into buttered pan.
Add boiled pierogi in a single layer to pan and avoid overcrowding. Cook until crisp and golden, 1 to 2 minutes per side. Repeat with remaining pierogi, adding more butter as needed.