Finely chop the dark chocolate.
Pour the heavy cream into a saucepan and heat over low heat.
Add the dark chocolate to the warmed cream and let it melt.
Mix until smooth, then let it cool at room temperature.
Pour the mixture into a square container and refrigerate for 2 hours until set.
Take the set chocolate out and cut into bite-sized pieces.
Sprinkle with cocoa powder to finish.