In a large mixing bowl mix the flour, cream cheese, egg, salt, and water. Turn onto a lightly floured surface and knead until the dough is soft and even.
Place the cooked potatoes in another large mixing bowl and mash. Add sauteed onions, cream cheese, paprika, garlic powder, salt, and pepper. Mix until texture is solid and not runny.
Roll dough approximately 1/8-inch thick. Cut into round shapes, approximately 3 1/2-inches in diameter. Add a small amount of potato filling to the center of a disk. Fold in half to form a half-moon shape. Seal and pinch ends tightly.
Bring a large pot of water to a boil. Boil pierogis rapidly for 4 to 5 minutes. Drain and cool.
Melt butter in a saute pan, add chopped onions, and cook until browned. Add the peirogis and saute until slightly crisp.
Professional Recipe: This recipe was provided by a chef, restaurant or culinary professional and makes a large quantity. The Food Network Kitchens chefs have not tested this recipe in the proportions indicated and therefore cannot make any representation as to the results.