Mix flour and salt together in bowl.
Stir in egg.
Add sour cream and butter and blend in.
You may have to start working the dough with your hands at this point.
Add flour as needed, and splash with a little lukewarm water.
When dough starts to hold shape, move to a cutting board or surface for kneading.
Add flour and continue to knead until it reaches the smoothness "of a baby's bottom."
Return dough to bowl and let it set up for about 10-20 minutes.
Divide dough into 2-3 sections.
Place one small section of dough on a floured cutting board.
Press dough down and flatten as much as possible.
Sprinkle a little flour on the top of the dough.
Roll out dough with rolling pin.
Flip dough, sprinkle with flour as needed, until dough reaches desired thickness.
Using a drinking glass or dough press, cut out circles of dough and set aside. Repeat process until all the dough is rolled and cut.
Take a dough circle, add a heaping teaspoon of filling in the center (could be more or less, depending on size of dough circle).
If using dough press, add a small amount of water around the edge of the dough, then close the press to seal.
Otherwise, add a small amount of water around the edge of the dough, press together with fingers, then use a fork to crimp the seal.
If eating right away, add pierogies to boiling water until they float, then move them to a pan with melted butter and onions, and fry until desired crispiness is reached.
If not eating immediately, spread pierogies on a cookie sheet and freeze until hard. Pierogies can then be placed in ziplock bags and stored for months--if they last that long!!!