To make the dough, mix the sour cream and eggs together in a large mixing bowl or the bowl of an electric mixer. Add flour and knead until smooth, but not sticky. You can use an electric mixer fitted with the dough hook attachment if desired. You may need to add a little more flour, bit by bit, until you get the dough to a smooth texture. Let rest 10 minutes, covered with a kitchen towel.
To make the filling, mix all the ingredients together, season with salt and pepper, and set aside.
Divide dough in quarters, and working with one quarter at a time on a surface lightly dusted with flour, roll dough thin (about ⅛-inch thickness).
Using a 4-inch round cutter (or the edge of a glass) dipped in flour, cut circles out of dough. Spoon filling slightly off center.
Moisten edge of circle with water, then fold, pressing edges together firmly. Crimp edges with fork tines. Repeat with remaining dough, re-rolling the scraps as needed. Set aside on a flour-dusted baking sheet until ready to cook.
Drop pierogies in salted, boiling water; cook 5 minutes (6 if frozen) then remove carefully with a slotted spoon. Toss with a little melted butter and serve.