Wikipedia
Streuselkuchen (, 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, butter 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 fruit (mostly of sour taste, e.g. apples, gooseberries, sour cherries, rhubarb), poppy seeds or creme or using a shortening-based dough.