A knish is a filled pastry that originated in Jewish communities in Eastern Europe. Knish is a Yiddish word derived from the Ukrainian or Russian "knysh", meaning dumpling or cake. In the 1890s, a Romanian immigrant named Yonah Schimmel began selling his wifes knishes from a pushcart at Coney Island, and in 1910 Schimmel opened a knishery on Manhattan’s Lower East Side. Knishes were originally baked, and filled with either a potato filling or a kasha filling. Kasha is a whole-grain filling that usually consists of buckwheat groats. Later someone got the idea of frying them, and found that they held together better when fried, which made them easier to handle by New york street vendors. Today, they may be either baked, grilled, or deep fried. Although potato filled knishes are still the most popular, they may be filled with a variety of savory and sweet fillings. Knishes may be round or square. The baked ones are usually round, and the square ones are usually fried. Knish purists prefer the baked ones.
There is a knish fansite here: Knishery NYC
Knishes, Buying Online
Knishes, Gabila's Square Fried
Knishes, Brooklyn Style Baked
Sam's Coney Island Knishes
You can buy frozen knishes online. Your supermarket might have them, also.: