For the dough: Mix the eggs, egg yolk, sour cream and 1/2 cup water together in a bowl.
In another bowl, combine the flour and 2 teaspoons salt.
Mix the wet ingredients with the dry ingredients, adding the remaining 1/2 cup water slowly and in increments until the mixture is adequately hydrated. Mix until soft and smooth texture.
Cover dough. Refrigerate for 15 minutes.
For the filling:
Preheat the oven to 180 degrees F. Peel and cut potato into thirds and place into a large saucepan. Bring the water to a boil and cook until fork tender.
Place the potatoes on sheet trays and place in 180-degree oven until all moisture has been released and no more steam rises.
Small dice and caramelize the onions in a large skillet. Add the potatoes, cheese and egg yolks; stir to combine. Season with salt and pepper.
Using a pasta sheeter attachment on a stand mixer (recommended: Kitchen Aid) or using a rolling pin, sheet the pierogi dough to setting number 3 or to your desired thickness.
Using a rim of a glass, cut out circles into the sheets of dough.
Place the maximum amount of filling into the cut-out circle that will allow you to fold over the dough, pinch the edges, and shape into half moons.
Bring a saucepot with water to a boil, and put the pierogi inside and poach on a rapid simmer for 2 to 3 minutes.
Alternatively you could pan-fry your pierogis in clarified butter or canola oil.
Eat and enjoy the pierogis!
This recipe was provided by professional chefs and has been scaled down from a bulk recipe provided by a restaurant. The Food Network Kitchens chefs have not tested this recipe, in the proportions indicated, and therefore, we cannot make any representation as to the results.