Break the two types of chocolate into pieces in a bowl. Heat the liquid cream in a saucepan. Bring to a boil, pour over the chocolate, then mix to smooth. Flavor with rum. Break the eggs, separating the whites from the yolks. Whip the yolks with the powdered sugar and vanilla sugar until whitened. Gradually incorporate the chocolate cream. Beat the egg whites until stiff, then gently fold into the mixture. Divide the mixture evenly between two cups. Refrigerate for at least 6 hours. Serve fresh, after sprinkling the mousses with a cloud of praline.