Pierogis

Pierogi dough made with egg and sour cream. It becomes tender, ridiculously stretchy and easy to press together and seal. 

Filling is two types combined: mashed potatoes with cheese ↑ added and Pennsylvania-Dutch style sweet/sour cabbage ↓, here with sausage and diced mushroom. Either filling is fine by itself. 

Boiled until they float, a minute at most, then fried in butter with sage.