Make a mound out of the flour, then make a well in the center.
Place egg yolks and eggs in the center, cutting in the flour with a knife and adding water and salt. Knead until firm. Cut in three parts. Roll dough out thinly, then cut circles with a cup. Place small amount of filling off center on each circle of dough. Fold over and seal by moistening edge with water and putting pressure on edges for a firm seal.
Boil a pot of water. Add salt. Drop pierogi into boiling water.
Cook lightly for 5 minutes uskng a low flame. Remove gently with strainer spoon and brown in butter in frying pan. Serve with sour cream.
Drain cottage cheese. Combine ingredients and mix until smooth. Fill circles of dough with desired amount.
Can also use potatoes, meat, sauerkraut, prunes, mushrooms or combinations of these to fill pierogi.