HEAT oven to 350°F. Mix dry cake mix, margarine and 1/3 cup milk until blended; press two-thirds onto bottom of 13x9-inch baking pan. Bake 12 to 14 min. or until centre is almost set; cool 3 min.

MIX peanut butter and remaining milk; spread peanut butter mixture onto crust. Top with spoonfuls of marshmallow creme and remaining cake mixture. Sprinkle with nuts and chocolate; press gently into cake mixture.

BAKE 18 min. or just until centre is set. Cool completely before cutting into bars.