Whip the whipped cream until stiff. Beat the egg whites until stiff. Stir the egg yolks until creamy, add cocoa powder, sweetener and flavorings and stir well again. Add 1 tablespoon each of egg white and cream to the chocolate mixture and stir again. Add the remaining egg white and cream to the chocolate cream and fold in (do not stir) until a smooth, fluffy cream is formed.
Pour the chocolate mousse into a bowl or dessert bowl and chill in the refrigerator overnight, if possible.