I’m going with fondant because it’s traditional. Yes, I know there are a lot of bakeries our there that are updating the black and white these days, using coatings of melted chocolate, ganaches and/or thick applications of frosting. To me that’s taking a good idea too far. I’ve long maintained that good cake needs very little adornment…a thin application of a real buttercream or a delicate veneer of icing. Any more and you ruin a delicate balance. The genius of a good black and white is that there’s just enough of the sweet stuff on the top to entice you into another bite. Which is why most of us have very little trouble finishing off the whole thing.