Jelly-filled donuts have an interesting history. They are variously called Berliners by German and paczki by Poles. No one really knows where or how they originated. Although some trace it to a 1485 cookbook, Kuchenmeisterei (Mastery of the Kitchen), which gives a recipe consisting of jam sandwiched between two rounds of yeast dough bread and deep-fried in lard. Then, sometime later, someone got the idea of injecting jelly into deep-fried donuts. In the upper Midwest, jelly donuts are called "jam busters, and are extremely popular. If you're fan of any kind of donuts, these suckers are delicious.