In heavy saucepan over very low heat or a double-boiler over simmering water, melt chocolate. Reserve and allow to cool slightly. In heavy saucepan over very low heat or a double-boiler over simmering water, whisk egg yolks and water until mixture begins to thicken. Whisk in cognac; continue to whisk until mixture has thickened to the consistency of Hollandaise sauce. Remove from heat and whish in melted chocolate. Set aside. In small bowl of an electric mixer, beat cream just until it holds soft peaks. If chocolate mixture has stiffened, heat gently over very low heat, whisking constantly, until slightly softened. Transfer mixture to a large bowl; whisk in 1/2 cup of the whipped cream. Fold in remaining whipped cream with a large whisk or spatula, them cut through with a spatula or curved fingers to eliminate large air bubbles. Set aside. Beat egg whites until they hold soft peaks. Beat in sugar (if used) just until mixture holds stiff peaks. Stir a small amount of the egg whites until chocolate mixture to lighten it; then fold in remaining egg whites. Spoon into a serving bowl or 8 small molds. Refrigerate at least 4 hours or until firm. Garnish just before serving with chocolate curls, if desired. This is best eaten the same day as prepared. Makes 8 servings. File ftp://ftp.idiscover.co.uk/pub/food/mealmaster/recipes/mmkah001.zip