Start by making the chocolate ganache` by melting the cream and chocolate together in a saucepan over a low heat, stirring constantly. When the chocolate has melted, take the saucepan of the heat and mix in the rum. Pour the chocolate sauce into a bowl and leave to cool in the fridge for an hour or two. To make the chocolate macaroons, whip the egg whites to stiff peaks. Next, sift in the icing sugar and cocoa powder, and add in the ground almonds. Gently fold the dry ingredients into the stiff egg whites, keeping in as much air as possible. Place the mixture into a piping bag, and pipe small rounds onto baking trays lined with non-stick oven paper. Bake in the oven immediately at 180`c, for roughly 20 minutes. Remove the cooked macaroons from the oven, and leave to cool completely on the baking tray. Next, remove the chocolate ganache from the fridge and use it to sandwich the chocolate macaroons together.