Cut the chocolate into small pieces and melt in bain marie. When the chocolate is thoroughly melted take off the heat and leave to one side. Whisk the egg whites either by hand or with a mixer until they form a meringue - soft like peaks. Gradually add the sugar to the meringue mixture and continue whisking until the meringue mixture is glossy and has firm peaks. Take one table spoon of the meringue mixture and add this into the melted chocolate and fold gently with a spatula. Add the vanilla liqueur and continue to fold gently. Add the melted chocolate to the rest of the meringue and continue to fold with your spatula until the mixture comes together and is completely combined. Finally add the cream and stir in gently until this well blended. Spoon the mousse into 4 dessert cups and chill in the refrigerator for 2-3 hours. Garnish with small pieces of chopped chocolate, icing sugar and fresh mint.