In a large bowl, whisk together the flour and 1/2 teaspoon of salt. Make a well in the center and add the egg, oil, and warm water.

Mix the dough until it comes together, then knead on a floured surface for about 5 minutes until smooth and elastic. Cover with a towel and let rest for 30 minutes.

While the dough rests, boil the peeled potatoes in salted water until tender, about 15 minutes. Drain well and mash until smooth.

In a skillet, cook the chopped onion in a little bacon fat or butter until caramelized and soft. Add this to the mashed potatoes.

Stir the shredded cheddar cheese and crumbled bacon into the warm potato mixture. Season with remaining salt and pepper to taste. Let the filling cool slightly.

Roll out the dough on a floured surface to about 1/8 inch thickness. Use a round cutter or glass to cut out 3-inch circles.

Place a tablespoon of filling in the center of each circle. Fold the dough over to create a half-moon shape and pinch the edges tightly to seal.

Bring a large pot of salted water to a boil. Drop the pierogi in batches and cook until they float to the top, then boil for an additional 2 minutes.

Remove pierogi with a slotted spoon. For a crispy finish, melt butter in a skillet and fry the boiled pierogi for 2-3 minutes per side until golden brown.

Serve hot with a dollop of sour cream and fresh chives.