MIX Crust Mix, sugar and margarine with fork in 9-inch pie plate until well blended. Press firmly against side of pie plate with fingers or large spoon to shape the edge, then press remaining crumbs firmly onto bottom of pie plate with dry measuring cup.
MICROWAVE chocolate and 2 Tbsp. of the milk in microwavable bowl on HIGH 1-1/2 minutes or until chocolate is almost melted. Stir until chocolate is completely melted.
BEAT remaining cold milk and Filling Mix with electric mixer on low speed just until blended. Beat on medium speed 3 minutes. (Filling will be thick.) Spoon 2 cups of the filling into crust. Stir chocolate mixture into remaining filling; spoon over cheesecake. Cut through batter with knife several times for marble effect. Refrigerate at least 1 hour. Store leftover cheesecake in refrigerator.