In the bowl of a stand mixer combine the flour and salt, making a well in the middle. Add the egg and mix on low speed until just combined. Add the sour cream and butter and mix until fully incorporated, about 3 minutes.

Turn the dough out onto a clean, lightly floured workspace and knead until smooth, about 1 minute. Wrap the dough in plastic wrap and refrigerate for 1 hour.

In a large pot over medium-high heat, bring water to a rolling boil. Cook the potatoes until they are tender, stirring occasionally, about 20 minutes. Drain the potatoes completely. Add the potatoes to the bowl of a standing mixer or a large bowl if using a handheld mixer.

Add the cream and cheese, mixing on medium speed until smooth, about 2 minutes. Add the chives and season with salt and pepper, stirring to combine.

On a clean lightly floured work surface roll the dough out 1/8-inch thick. Use a 3½ -inch circular cookie cutter to cut the dough. Working one at a time, fill each circle with about 1 tablespoon of the filling. Fold the edges around the filling in a half-moon and press with your fingers to seal shut. Use a fork to help seal them and create decorative edges.

Set aside on a lightly floured baking sheet and repeat the process with the remaining dough and filling.

Bring a large pot of water to a boil over high heat. Add the pierogies about 10 at a time so the pot is not overcrowded. Cook until the pierogi float to the top, about 1 to 2 minutes and use a slotted spoon to remove to a plate. Continue with the remaining pierogi.

Heat a large sauté pan over medium heat, add the oil and heat through. Add the onion and sauté, stirring occasionally until the onions are golden brown, about 10 minutes. Remove and set aside in a bowl.

Return the pan to medium heat and add 2 tablespoons of the butter and allow to melt. Working in batches as to not overcrowd the pan add pierogies and cook until crispy and golden brown, about 2 minutes on each side. Remove and repeat with the remaining butter and pierogi.

Arrange pierogi on a platter topped with onions and chives with sour cream on the side for dipping.