Divide dough into 2 pieces. Cover the second piece with the mixing bowl and thinly roll the first piece out onto a floured surface to just under 1/8 thickness.
Use a 3" diameter round cookie cutter to cut circles from the dough, keeping them as close as possible (collect scraps and place under the bowl to re-use) add 1/2 tbsp of potatoes over each round.
To form pierogi, pull the 2 edges together and pinch tightly to seal. To ensure a tight seal, crimp the edges a second time with a pinch and twist motion.