Combine butter and peanut butter in a medium, microwave-safe bowl. Heat in the microwave until soft; mix well. Gradually stir in confectioners' sugar until mixture resembles a soft dough. Spread mixture into two prepared pie crusts.
Mix milk with instant pudding in a small bowl; pour over peanut butter mixture in each crust. Chill until firm.
Top pies with whipped topping when ready to serve.
