Prepare cake batter and bake in 13x9 pan as directed on package. Cool cake in pan 10 min, then pierce cake with large fork at 1/2 inch 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 necessar until milk mixture is absorbed. Refrigerate 1 hour. Meanwhile, make curls from remaining chocolate.
Stir cocoal into cool whip. Frost cake with cook whip, top with chocolate curls.
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