Wikipedia
Bierock (pronounced somewhere between "brock" and "brook" in Nebraska and "beer-rock" in Kansas and Oklahoma) is a yeast dough pastry pocket sandwich with savory filling, originating in Eastern Europe, possibly in Russia. The dish is common among the Volga German community in the United States and Argentina. It was brought to the United States in the 1880s by German Russian Mennonite immigrants. Other spellings are bieroch, beerock, berrock, bierox, beerrock and kraut bierock in the U.S, and pirok or kraut pirok in Argentina.
Bierock is filled with cooked and seasoned ground beef, shredded cabbage and onions, then oven baked until the dough is golden brown. Some variants include grated carrots.
Bierocks are similar to both pirogi/ pirozhki of Russian cuisine and börek of Turkish cuisine. There is debate about the actual etymology of the word bierock. Traditionally it was supposed that bierock was derived from the Russian word pirog. However, a recent theory speculates that the word bierock may be derived from börek. This theory is based on both geographic close proximity of the former Volga German ASSR to present day Kazakhstan as well as the influence of considerable population of historically Turkic speaking peoples such as Kazakhs and Tatars living in the Volga region. Neither theory, however, has been conclusively proven.
In Argentina, the Fiesta del Pirok (Bierock Festival) takes place every July, in Crespo, Entre Ríos Province.