Grease three 23 cm round cakepans, and line with wax paper. Grease and flour wax paper. Set aside. Combine half cup sugar, water, and chocolate in a small saucepan; cook over low heat, stirring constantly, until chocolate melts. Cool. Cream butter; gradually add remaining 2 cups sugar, beating well at medium speed of an electric mixer. Add egg yolks, one at a time, beating after each addition. Stir in vanilla and chocolate mixture. Combine flour, soda, and salt; add to creamed mixture alternately with milk, beginning and ending with flour mixture. Mix after each addition. Beat egg whites until frothy; add cream of tartar, and beat until stiff peaks form. Gently fold into batter. Pour batter into prepared cakepans. Bake at 180ºC or 25 to 30 minutes or until a wooden pick inserted in center comes out clean. Cool in pans 10 minutes; remove from pans, and let cool completely on wire racks. Spread Mocha Frosting between cake. ----