Knead the butter, sugar and flour and a pinch of salt together and divide the dough in three parts. Add the cacao to one part. Put the dough in the fridge for half an hour. Roll both the white and the brown dough into two long thin rolls, so you have four rolls. Lay a brown and a white one together and glue them with egg white. Put a brown one on top of the white and a white one on top of the brown, use some egg white again. Roll out the remaining dough into a thin rectangle and fold it around the cookie bar. Now cut slices and brush these with egg whites. Put them on the oven tray. Bake 15 minutes at 180 degrees Celsius.

These cookies look very similar to chessboard cookies, but the composition is different.