Heat oven to 350°. In a large bowl, combine wafer crumbs and sugar; mix in butter until crumbs are moistened. Press crumbs into a 9-inch pie plate. Bake at 350° for 15 minutes; cool.
Place chocolate chips in a small bowl; microwave on high 1 minute. Stir until smooth. In a medium bowl, combine sour cream, liqueur, sugar and vanilla. Stir in melted chocolate; spread evenly over cookie crust. Freeze 2 hours.
In a medium bowl, whisk together whipped topping and cocoa powder; fold in mini chunks. Swirl mixture over pie and freeze overnight.
Let stand 10 minutes before serving.