4 cups all-purpose flour, plus extra for flouring your work surface
1/2 teaspoon salt
3 tablespoons salted butter, melted
1 cup sour cream
1/8 cup corn oil
2 whole eggs
1 egg yolk
Two russet potatoes, peeled and mashed
1 cup cheese, grated
All-purpose flour for sprinkling and flouring work surfaces and dough
4 tablespoons butter
Combine the flour and salt in the bowl of a stand mixer fitted with the dough hook. In a separate large bowl, combine the melted butter, sour cream, and corn oil. Beat the eggs and egg yolk together, and add them to the sour cream mixture. Whisk everything together well, so it forms a smooth, thick liquid.
Add the wet mixture to the flour in the mixer bowl, and mix on low speed for about a minute and a half, until you’ve got a thick dough.
Sprinkle some flour on your work surface, and knead the dough by hand, forming it into a ball. Then use a rolling pin to roll the dough out into a thick disk about the size of a Frisbee, or push it into this shape with your hands. (This will make the dough easier to work with when it’s cold.) Wrap the dough well in plastic wrap and chill it in the fridge for at least 6 hours.
Combine the mashed potatoes and cheese in a bowl and set aside.
Preheat the oven to 175 degrees F.
Take the dough out of the fridge and let it come up to room temperature on the countertop until it’s soft enough to work with (about 20 minutes).
Whisk the eggs together in a small bowl.
Flour a work surface well. Using a rolling pin, roll out the dough in batches, turning it and rolling in every direction, including diagonally, until it’s basically the same thickness as one of the cookies in an Oreo. Use a round pastry cutter (or the mouth of a glass) to cut out as many rounds as possible from each piece of dough.
Using a pastry brush, lightly brush the top of each round of dough with the egg (so it will stick together when you close it up). Take the filling out of the fridge just before you’re ready to use it.
Put 1 tablespoon of the filling on the middle of each round. Then fold the round in half around the filling, so you’ve got a half-moon with the filling inside. Use your fingers to pinch the open sides closed all the way around, making little pinches all the way along the edges.
Put a large pot of well-salted water on to boil. While the water is heating, put the pierogies on a tray in the fridge so they cool down a little and the dough sets.
When the water comes to a boil, put the first batch of pierogies in the pot about 8-10 at a time. The pierogies will take about 7 minutes to cook, depending on your stove and the thickness of your dough. They’re definitely not done until they float up to the top, and then they probably need another minute or two. The best way to know if they’re ready is to take one out, cut it open, and taste it.