In baking and pastry making, streusel (German pronunciation: [ˈʃtʁɔʏzəl]) is a crumbly topping of flour, butter, and sugar that is baked on top of muffins, breads, pies, and cakes.[1] Some modern recipes add spices and chopped nutmeats. The mixture can also be layered or ribboned in the middle of the cake.