Coarsely chop the chocolate and melt over a hot, not boiling, water bath. Remove from the heat and let cool. Separate the eggs. Beat the egg whites with the sugar until stiff. Beat the egg yolks with the vanilla sugar over the hot water bath until creamy and the sugar has dissolved. Remove from the heat, stir in the chocolate and stir over a cold water bath until cold.
Beat 100 ml (approximately 0.5 cup) of cream until stiff and fold into the cooled mixture. Gently fold in the egg whites.
Pour the chocolate mousse into glasses and chill for 2 hours.
Beat the remaining cream until stiff and spread on the chocolate mousse. Serve sprinkled with chocolate shavings.