Streuselkuchen/Kołacz (crumb cake) is a German specialty. Traditionally it is made of a yeast dough covered with a sweet crumb topping referred to as streusel. The main ingredients for the crumbs are sugar, fat and flour, which are mixed at a 1:1:2 ratio.
German Streuselkuchen is usually a flat cake made on a baking tray and cut into oblong pieces. It should be very flat - about one inch - so crumbs make about 50 percent of its height. Yeast dough is the original, a short crust is possible too, a puff pastry at the bottom turns it into a "Prasselkuchen".
The recipe allegedly originated from Silesia, a province that is nowadays in Western Poland, but the cake is found everywhere today. Many variants are prepared, with fillings such as fruits and creme, or using a shortening-based dough.