In a large bowl, cream butter and confectioners' sugar until light and fluffy, about 5 minutes. Gradually add flour and cornstarch, beating until well blended. , With hands lightly dusted with additional cornstarch, roll dough into 1-in. balls. Place 1 in. apart on ungreased baking sheets. Press lightly with a floured fork. Top with nonpareils or cherry halves. , Bake at 300° until bottoms are lightly browned, 20-22 minutes. Cool for 5 minutes before removing from pans to wire racks.