Break the chocolate into small pieces. Heat carefully with 150 g of cream in a saucepan until the chocolate has melted. Stir the mixture until smooth and remove from the stove.
Beat the rest of the cream until stiff. Slowly fold the icing sugar, rum and chocolate mixture into the whipped cream and stir. If you use milk chocolate, leave out the powdered sugar, otherwise the cream will be too sweet.
Spread the cream on dessert bowls or long glasses. Cover with cling film and put in the refrigerator for 1 - 2 hours.
Before serving, pour chocolate curls or flakes over the cream. If you like, you can sprinkle some grated peel of an orange on top of the chocolate.