Put the chocolate pieces in a large, stainless steel mixing bowl. Set aside.
Heat the cream over medium heat and bring to a boil. Pour the cream over the chocolate and allow it to stand for 5 minutes.
Whisk together until smooth and stir in the butter. Allow it to cool.
To make the macaroons : line 2 baking sheets with parchment/ greaseproof paper.
Whisk together the icing sugar, ground almonds and cocoa powder ensuring no lumps remain.
Beat the egg whites with an electric mixer, gradually adding caster sugar, until firm peaks form. Gently fold into the sugar, almond powder and cocoa powder mixture.
Spoon the mixture into a piping bag and pipe one inch circles, an inch apart, onto the lined baking tray. Set aside for 30 minutes before baking in a preheated oven at 180 degree celsius for about 18 minutes.
Allow the macaroons to cool completely before removing from the baking tray.
Spread some of the chocolate filling on the flat side of the macaroons and sandwich with another circle. Repeat process with the remaining macaroons.
Serve immediately or refrigerate in an airlight container. You can store them for approximately 3 days.