Sift the flour into a large bowl, then add to a blender. Add the sugar, 200g of butter, eggs, 1 tablespoon of milk, baking powder and vanilla into the blender. Blend until smooth.
Pour into 2 greased tins and place into a preheated oven at 170 C / Gas 3 for 20 minutes, or until the cake has started to pull away from the edges of the tins, and a knife slides out without any cake mixture on it.
Wait until cool, and then mix icing sugar, 60g of butter, cocoa powder and 1 tablespoon of milk (or as much as needed to create a smooth consistency) in a blender.
Ice the top of both cakes, and then place one on top of the other. Use the remaining icing to cover the sides of the cake.
Cut the mini rolls into thin slices, and decorate the top in circles (you could do the sides as well if you have enough rolls).
I found the mini rolls easier to cut once they'd been in the fridge, but don't worry if the chocolate flakes off, you can't help that!