Prepare the pudding according to packet instructions. Allow to cool to room temperature, about 15-20 minutes. Stir every 3-4 minutes or cover with plastic wrap to prevent a skin from forming.
While the pudding cools, whip the cream with the vanilla sugar until stiff peaks form. Grate the chocolate coarsely, setting aside roughly 1/4 for decoration.
Once cooled, stir the rum to taste and most of the grated chocolate into the pudding.
Fold the whipped cream into the pudding gently until combined. Divide into serving bowls and top with the reserved chocolate.