Preaheat oven to 350.
Prepare and bake cake mix as directed on package in 2 greased and floured 9-inch round cake pans. Cool 10 minutes; remove from pans. Cool completely on wire racks.
Meanwhile, pour milk into medium bowl. Add dry pudding mix. Beat 2 minutes, or until well blended. Add peanut butter; beat well. Refrigerate until ready to use.
Mix peanuts and melted chocolate; stir until evenly coated. Drop by tablespoonfuls onto waxed paper-covered baking sheet. Refrigerate 10 minutes, or until firm.
Place one of the cake layers on a cake platter; spread with 1 cup of the pudding mixture. Cover with rmaining cake layer. Gently stir whipped topping into remaining pudding mixture. Spread over top and side of cake. Decorate with chocolate peanut clusters. Store leftover cake in refrigerator.