Chocolate Peanut Butter Mallow Bars

1 pkg. (2-layer size) devil's food cake mix
1/2 cup (1 stick) butter, melted
2/3 cup milk, divided
3/4 cup creamy peanut butter
1 jar (7 oz.) JET-PUFFED Marshmallow Creme
1/2 cup PLANTERS Salted Peanuts
6 squares BAKER'S Semi-Sweet Chocolate, coarsely chopped
HEAT oven to 350°F. Mix dry cake mix, butter and 1/3 cup milk until blended; press 2/3 onto bottom of 13x9-inch pan. Bake 12 to 14 min. or until center is almost set; cool 3 min. Meanwhile, mix peanut butter and remaining milk.

SPREAD peanut butter mixture onto crust; top with small spoonfuls of the marshmallow creme and remaining cake mixture. Sprinkle with nuts and chocolate; press gently into cake mixture.

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