mmmm, ganache!! Put 2 parts chocolate (dark or milk) in a heatproof bowl. Bring 1 part pure cream to the boil then pour over chocolate and stir until chocolate is melted and its combined. Set aside to cool and thicken then spread on cake. Yummmmmm. Because you are boiling the cream, you can leave it out at room temp without the ganche going off. You can even make the ganache a coupe of days before and keep it in the fridge - just zap it in the microwave at 10sec intervals to bring it back to a spreading consistancy. A tip for icing too is to put the cake on a cooling rack, then ice so that all the drips fall through and the cake doesnt end up in a big puddle of icing. Omg, i want mud cake now!!