Ganache is a smooth emulsion of chocolate and hot cream — nothing more, at its simplest — that sets into a rich, spreadable or sliceable mass as it cools. It is the universal building block of the chocolatier's craft: warm and fluid it is a pourable glaze, at room temperature it is a pipeable filling for truffles, bonbons and tarts, and whipped it lightens into a mousse-like frosting.