For the crumble mix together the flour, sugar and butter with a mixer; Finally add the muesli and work into crumbles.
For the dough, mix the butter and creme fraiche with the mixer until creamy. Gradually add sugar and salt while stirring until a bond is formed. Then stir in the eggs one by one (each egg about 30 seconds).
Mix the flour, baking powder and cocoa powder and stir into the dough briefly in 2 stages on a medium heat. Put the finished dough in a greased tin (30 x 40cm) and spread the crumble on top.