Directions for Frosting:
Combine the sugar, egg whites, water and cream of tartar in a large heavy saucepan over low heat or double boiler over simmering water. With a portable mixer, beat mixture on low speed for 1 minute. Continue beating on low speed over low heat until frosting reaches 160° F, about 8-10 minutes. Pour into a large bowl; add vanilla. Beat on high speed until frosting forms stiff peaks, about 7 minutes. Pipe or spread over top and sides of cake. If desired, garnish with chocolate curls.