Peel and quarter the potatoes.

Place the potatoes in a pot of cold water.

Bring the water to a boil and cook until the potatoes are tender, about 45 minutes.

While the potatoes are cooking, make the dough.

In a bowl, combine the egg, sour cream, salt, and flour.

Stir the ingredients together and then knead the dough for a couple of minutes.

Wrap the dough in plastic and let it rest for 30 minutes.

Remove the potatoes from the water and transfer them to a large bowl.

Mash the potatoes.

Stir in the farmer's cheese, American cheese, and butter until the mixture is creamy.

Divide the dough in half and roll out the first half to about 1/4 inch thick.

Cut out circles of dough using a glass.

Fill each circle with a teaspoon of potato filling.

Fold the dough over the filling and pinch the edges to seal.

Press the edges with a fork to create a decorative pattern.

Lay the pierogi on a sheet tray lined with a towel.

Repeat the process with the other half of the dough.

Bring the potato water back to a boil.

Boil the pierogi in batches until they rise to the top, about 3 minutes.

Transfer the pierogi to a platter with a slotted spoon.

Saute sliced onion in butter until golden brown.

Toss the pierogi with the sauteed onion before serving.