Roughly chop the chocolate and melt it on a warm water bath. Remove from the stove and allow to cool slightly. In the meantime, separate the eggs. Beat the egg yolks, sugar and vanilla sugar in a tall beaker with the whisks of the hand mixer until creamy. Whip the cream until stiff.
Beat the egg whites until stiff. Stir the whipped egg yolk into the chocolate. Mix in half of the cream immediately with the whisk. Fold in the remaining cream and then fold in the beaten egg white in portions. Pour into 4 dessert glasses and chill for about 4 hours. Melt the dark and white chocolate coating separately on a warm water bath. Spread the marbled chocolate on a marble board and let it dry. Scrape into rolls with a spatula. Chill for 1-1 1/2 hours.
Pour into 4 dessert glasses and chill for about 4 hours. Melt the dark and white chocolate coating separately on a warm water bath. Spread the marbled chocolate on a marble board and let it dry. Scrape into rolls with a spatula. Chill for 1-1 1/2 hours. Decorate Mousse au Chocolat with chocolate rolls and dust with cocoa
4 hours waiting time