1. Line an 8-inch square pan with foil, with ends of the foil extending over the sides of the pan.
2. Mix crust mix, butter and sugar until well blended. Press firmly into the bottom of the pan using the bottom of a dry measuring cup.
3. Beat the milk and filling mix with an electric mixer on low speed just until blended. Then, beat on medium speed for 3 minutes (filling will be thick).
4. Spread half of the filling over the crust. Stir the chocolate into the remaining filling, then spread over filling in pan. Sprinkle with pecans.
5. Freeze for 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 the freezer.