So, the recipe I used from a very (apparently) competent mummy blog was:
225g 70% choc, chopped and melted, into which you stir 1/4 cup of cocoa and 1/2 cup icing sugar (+ pinch of salt).
So, I've just made it and there's not even enough moisture to incorporate all the dry powdery stuff, let alone to create something pourable/moldable. This will never spread into a foil tray or into individual silicone cases.
Other than eating it with a spoon whilst watching Food Network..any suggestions?