So we did .... and here is how we did in in case you want to try. It was the best recipe I've ever used soo moist, sweet and sugary with a beautiful flavour.
It is taken from the "Chocolate Box" book, which has the scrummiest recipes in. I liked this one because it used real chocolate instead of cocoa (which I refuse to pay over £2 a tub for!).
It does tell you the recipe for chocolate butter icing but we just used normal icing sugar and coloured it.