Prepare chocolate cake according do directions on box. Pour batter into 2 round cake pans. Bake according to box directions. After they are finished baking, put on a cooling rack and freeze for 30min-1 hour. While cakes are freezing, combine butter (or margarine) and peanut butter in a large sauce pan. Cook over medium heat, stirring occasionally, until melted, but not boiling. Stir in powdered sugar and graham cracker crumbs, set aside. In a medium-sized microwave-safe bowl, combine chocolate chips and shotening and melt in microwave for about 2 1/2 minutes, stirring every 30 seconds until chocolate is melted and smooth.