LINE 8-inch square pan with foil, with ends of foil extending over sides of pan. Mix Crust Mix, butter and sugar until well blended. Press firmly onto bottom of prepared pan using the bottom of a dry measuring cup.
BEAT milk and Filling Mix with electric mixer on low speed just until blended. Beat on medium speed 3 minutes. (Filling will be thick.) Spread half of the filling over crust. Stir chocolate into remaining filling; spread over filling in pan. Sprinkle with pecans.
FREEZE 4 hours or overnight. Remove dessert from freezer about 10 minutes before serving. Lift dessert from pan using foil handles. Let stand at room temperature to soften slightly. Cut into 18 bars. Store leftover bars in tightly covered container in freezer.