Peel the potatoes and cut into quarters. Add them to a large stockpot with boiling water. Boil for 20 minutes or until tender and cooked through. Drain in colander and place back into the same pot, set aside. Saute the onion while potatoes are cooking.

Heat 2 tbsp olive oil in pan over medium heat. Add onion and saute for 10 minutes until golden brown and soft. Add the sauteed onions into the pot with the potatoes along with sour cream, melted butter, and salt. Mash the potato mixture with a masher or a a mixer.

Assemble the pierogi: Work with 3-4 dough wrappers at a time. Lay them out on a clean surface. Spoon a tablespoon amount of filling in the middle of each wrapper. Dab your finger in a small dish of water and encircle the edges of the wrapper (this will help the dough stick together.) Fold the dough in half and bring the edges together. Crimp the edges of each pierogi with a fork to make sure they are well sealed. Transfer to a parchment lined baking sheet or large plate. Repeat with remaining ingredients.

Cook the pierogi: Heat 3 tbsp of oil in pan over medium/low heat. Add 6-8 pierogi at a time to the pan, making sure you don't overcrowd the pan. Cook 2-3 minutes per side, until golden and crisp. Transfer to a paper towel lined plate. Repeat with remaining pierogi. Add additional oil as needed. Serve with sour cream and garnish with chives.