Step 1

To prepare the sauerkraut filling, melt the butter in a skillet over medium heat. Stir in the onion, and cook until translucent, about 5 minutes. Add the drained sauerkraut and cook for an additional 5 minutes. Season to taste with salt and pepper, then remove to a plate to cool.

Step 2

For the mashed potato filling, melt the butter in a skillet over medium heat. Stir in the onion, and cook until translucent, about 5 minutes. Stir into the mashed potatoes, and season with salt and white pepper.

Step 3

To make the dough, beat together the eggs and sour cream until smooth. Sift together the flour, salt, and baking powder; stir into the sour cream mixture until dough comes together. Knead the dough on a lightly floured surface until firm and smooth. Divide the dough in half, then roll out one half to 1/8 inch thickness. Cut into 3 inch rounds using a biscuit cutter.

Step 4

Place a small spoonful of the mashed potato filling into the center of each round. Moisten the edges with water, fold over, and press together with a fork to seal. Repeat procedure with the remaining dough and the sauerkraut filling.

Step 5

Bring a large pot of lightly salted water to a boil. Add perogies and cook for 3 to 5 minutes or until pierogi float to the top. Remove with a slotted spoon.