Place first 5 ingredients in top of a double boiler; bring water to a boil. Reduce heat to low; cook, stirring occasionally, until chocolate melts. Remove chocolate mixture from heat, and set aside. Beat powdered egg white and water in a large bowl at high speed with an electric mixer until soft peaks form. Gradually add sugar, and beat until stiff peaks form. Fold one-fourth of egg white mixture into chocolate mixture; fold in whipped cream and remaining egg white mixture. Chill