Prepare cake as directed on package. Bake in 9 x 13" pan according to directions. Cool cake in pan 10 minutes.; then pierce cake with large fork at 1/2" intervals. Melt 7 oz. chocolate as directed on package. Blend milks and sour cream in blender until smooth. Add melted chocolate; blend well. Pour over cake, re-piercing cake if necessary until milk mixture is absorbed. Refrigerate 1 hour.
Stir cocoa into Cool Whip. Frost cake with Cool Whip mixture; top with chocolate curls made from remaining chocolate (opt); keep refrigerated. ENJOY!!!