pkg. (8 squares) BAKER'S Semi-Sweet Chocolate, divided
pkg. (2-layer size) chocolate cake mix
pkg. (3.9 oz.) JELL-O Chocolate Instant Pudding
cup BREAKSTONE'S or KNUDSEN Sour Cream
tub (8 oz.) COOL WHIP Whipped Topping (Do not thaw.)
cup chopped PLANTERS Pecans, toasted.
MELT 2 chocolate squares as directed on package. Beat cake mix, dry pudding mix and next 4 ingredients with mixer until well blended. Add melted chocolate; mix well. Pour into 15x10x1-inch pan sprayed with cooking spray. BAKE 20 to 22 min. or until toothpick inserted in center comes out clean. Cool 10 min. MEANWHILE, microwave remaining chocolate squares and COOL WHIP in microwaveable bowl. Microwave on HIGH 1-1/2 min. or until chocolate is completely melted and mixture is well blended, stirring after 1 min. Cool 15 min.; spread onto cake. Sprinkle with nuts.