two answers. Stirring unwhipped double cream into cooled but not set melted chocolate makes ganache which is a wonderful cake filling. Google for exact instructions. If you want to be braver, whisk together equal parts of double cream and mascarpone cheese and get it very cold in the fridge, not freezer. melt your chocolate then allow that to cool to the point where it is just not starting to set. Fold the chocolate into the cold cream mixture and you will get a creamy chocolatey blend with shards of set chocolate in it.