PREHEAT oven to 350. Grease two 9 inch round baking pans. Chop 2 of the chocolate squares; set aside. Beat cake mix, pudding mix, eggs, sour cream, oil and water in large bowl with mixer on low speed until moistened. Beat on medium 2 min. Stir in chopped chocolate. Pour into prepared pans.
BAKE 30-35 mins or until toothpick comes out clean. Cool 10 mins and invert onto wire racks. Cool completely.
Place FROZEN Cool Whip and 6 remaining chocolate squares in microwave, on high for 1.5 mins or until choc is melted and mixture is smooth. Stir after 1 min. Let stand 15 mins to thicken. Ice middle with about 1/4 of the frosting, then spread remaining frosting over entire cake.
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