350g heavy cream (double cream)
500g semisweet/bittersweet chocolate (finely chopped)
Method 1) Heat the cream UNTIL boiling point. Turn off heat. Pour over the chocolate and mix until smooth and shiny.
Method 2) Combine both ingredients in a bowl and heat over a double boiler (bain marie). Stir until smooth and shiny.
Allow to cool and refrigerate for half an hour at least, until it becomes viscous. (Such as Nutella spread, but a little thicker than that.)
It is now ready for use.