Combine flour and salt in an electric mixer for 30 seconds. In a large bowl, combine eggs, oil, and 3 cups of water. Put electric mixer on a slow speed and add sour cream and egg mixture to the flour mixture. Mix for about 2 1/2 minutes. At this point check the dough and make sure it is creamy and pliable, if it is too sticky, add a bit of flour, if it is not pliable add more water. When dough reaches desired texture, remove from the mixer and let rest on a floured table, covered with plastic wrap, for about 30 minutes.
After 30 minutes, begin working the dough with a floured rolling pin. Roll dough out to a rectangular shape that is 1 to 1 1/2-inches thick. Cut this into quarters. Take 1 sheet and roll out to 1/4-inch thickness. If dough begins to stick, sprinkle it with a bit of flour. Using a 2 to 3-inch cookie cutter, cut dough into circles.
Once circles are cut, roll the circles to 1/8-inch. Place 1 tablespoon of the desired filling in the center of each circle. Lightly wet 1/2 of the edge of the circle with water, fold over and crimp together.
Gently place pierogi into hot salted water that is just under boiling point, about 190 degrees F, and cook for 3 minutes or until pierogi float. Drain.
Melt butter in a large frying pan. Add pierogis and cook until golden brown. Serve with Sauteed onions, a dollop of sour cream and chopped chives.