Pirogi 

12 ounces Yukon Gold potatoes (about 2 medium), peeled, cut into 1" pieces
12 ounces kielbasa, casings removed, cut into ½" pieces
⅔ cup drained sauerkraut
½ teaspoon caraway seeds
egg-enriched pie dough (homemade or commercial)
1 large egg, beaten
½ cup unsalted butter, divided
2 tablespoons olive oil
kosher salt
1 medium onion, sliced, for serving
sour cream, for serving

Boil potato pieces, and mix with kielbasa, sauerkraut and caraway seeds to form filling. Set aside.

Flatten dough, and cut into circles. Brush beaten egg around outer edge of each circle to help seal the crust. Place filling in the center of each circle, and fold dough in half. Use a metal table fork to press the edges of each semicircle down and seal the dough. Cut away excess dough to leave ½" flat edge around each pirogi.

Melt half the butter, add olive oil, and fry the pies on both sides until golden brown.

Using a second fry pan, melt remaining butter and fry sliced onion until caramelized. Garnish each serving of pirogi with ½ cup of fried onion and 2 tablespoons sour cream, and serve immediately.