For the dark mousse, melt the chocolate in the coffee at low temperature, stirring constantly. Separate the eggs, beat the egg yolks with the sugar and vanilla sugar with a mixer until very creamy. Gradually fold the chocolate into the egg cream while stirring. Let everything cool together until it starts to firm up. Separately, whip the egg whites and whipped cream until stiff. Carefully fold the cream into the crème, then the egg whites.
For the white mousse, soak the gelatine in cold water. Break the chocolate into pieces, melt it with half of the whipped cream and the arrack in a saucepan at low temperature, stirring. Separate the eggs, beat the egg yolks with the vanilla sugar and a tbsp. of warm water with the whisk of a mixer until creamy. Squeeze the gelatine, let it melt in the warm chocolate while stirring, fold the mixture into the egg cream. Let everything cool together until it starts to firm up. Separately, whip the egg whites and the remaining whipped cream until stiff. First fold the whipped cream, then the egg whites carefully into the white cream. Alternate the white and dark mousse in four to five layers in a glass bowl, then carefully pull a fork through the crème and set aside to cool. Just before serving, decorate with shaved chocolate.
Tip: Do you prefer milk chocolate or dark chocolate? Depending on the case, use whichever you like better.