RITZ Bits and Mini OREO Smash-Up Bars

Line 13x9-inch pan with foil, with ends of foil extending over sides; spray with cooking spray.

Combine RITZ Bits and cookies.

Microwave butter in large microwaveable bowl on HIGH 45 sec. or until melted. Add marshmallows; stir to evenly coat marshmallows with butter.  Microwave 1 min. or until marshmallows are completely melted and mixture is well blended, stirring every 30 sec.

Reserve 1/2 cup RITZ Bits mixture for later use.  Add remaining RITZ Bits mixture to melted marshmallow mixture along with the popcorn; mix well. 

Press popcorn mixture onto bottom of prepared pan. Sprinkle with reserved RITZ Bits mixture; press gently into popcorn mixture to secure. Cool completely.

Use foil handles to remove popcorn mixture from pan before cutting into bars.