Black part: Ground biscuits in mixer to get fine powder, add powder sugar, melted chocolate (or cocoa powder) and add milk little by little until you get solid mass. Place in the fridge.
White part: Melt the butter, using hand mixer mix it with powder sugar and add coconuts powder. Place in the fridge.
Place baking sheet in the working surface and then spread black part (you can use cling film over it) in rectangle shape with a rolling pin(one side longer than the other), and then white part over it.
Start rolling from the longer side, press slightly until the end so you get a roll.
Make chocolate glaze using double boiling system. Spread the glaze over cake, sprinkle coconut powder over it and put in the fridge until cold. Overnight is better.
Cut in even pieces around 1-2cm thick and serve. It can stay in the fridge for 5days.
Milk for black part, should be added gradually. Butter for white part, should be softened.