Wikipedia knows something about pierogi

Pierogi (/pɪˈroʊɡi/ pih-ROH-ghee) are filled dumplings of Central and Eastern European origin, made by wrapping unleavened dough around a savory or sweet filling and cooking in boiling water, or pan-frying. Pierogi which consist of noodle dough and have to be cooked in boiling water are associated with the Central and Eastern European kitchens where they are considered national dishes especially in Poland. Pierogi-like dumplings are popular in most Central and Eastern European countries as well as in Ashkenazi Jewish and modern-day American cuisines, where they are known under their local names.

Typical fillings include potato, sauerkraut, ground meat, cheese and fruits. The dumplings may be served with a topping, such as melted butter, sour cream or fried onion, or a combination of those ingredients.