These are quite similar to Polish Pierogies, with a slightly different shape, and available with various potato fillings (with or without bacon, dill, etc), or as pictured below, with fruit or cream cheese. Vareniki have a pasta type shell that is filled, and then boiled to be served hot with butter and/or sour cream as a main dish (potato varieties) or fruit or cheese varieties can be topped with whipped cream (or butter and sugar or both!) as a great breakfast or dessert.
Vareniki are sold frozen by the dozen. Home preparation is as easy as bringing a pot of salted (just a pinch) water to a boil, and cooking for 7 minutes (potato) or 5 minutes for fruit.