PREHEAT oven to 350°F. Grease and flour 9-inch round cake pan; line bottom with wax paper. Microwave 4 squares of the chocolate and butter in large microwaveable bowl on HIGH 1-1/2 to 2 min. or until chocolate is almost melted, stirring after 1 min. Stir until chocolate is completely melted. Stir dry gelatin mix and sugar into chocolate until well blended. Mix in eggs. Stir in flour and pecans until well blended. Pour into prepared pan.

BAKE 40 min. or until toothpick inserted in center comes out with fudgy crumbs. (Do not overbake.) Cool in pan 5 min. Run small knife around side of pan to loosen edge. Invert onto serving platter; remove wax paper. Cool cake completely.

MELT 4 squares of the remaining chocolate in microwave on HIGH 1-1/2 min. or until melted, stirring after 1 min. Stir until chocolate is completely melted. Spread on wax paper-covered baking sheet; refrigerate 30 min.

MEANWHILE, melt remaining 4 squares chocolate in microwavable bowl on HIGH 1-1/2 min. or until melted, stirring after 1 min. Stir until chocolate is completely melted; stir in whipped topping until smooth. Frost cake with whipped chocolate mixture.

REMOVE chocolate on baking sheet from refrigerator; using sharp knife, cut into 1-1/2- to 2-inch irregular-shaped pieces. Remove chocolate pieces from wax paper; arrange on top of cake. Store cake in refrigerator.