In a medium bowl, add the melted butter, pretzel crumbs, confectioners' sugar and 1 cup of the peanut butter and stir together until well combined. Press the mixture evenly into the bottom of an ungreased 9-by-13-by-2-inch baking dish. Combine the chocolate chips and the remaining 1/4 cup peanut butter in a microwave-safe bowl. Microwave in 30-second intervals, stirring in between, until the chocolate and peanut butter are melted and smooth; two intervals should be enough. Mix to blend, then spread over the peanut butter-pretzel layer. Refrigerate for at least 1 hour before cutting into squares.