In large bowl, cream butter and sugars until light and fluffy.
Combine flour, cornstarch and salt; gradually add to creamed mixture and mix well.
Roll dough into a 15x2x1-in. rectangle; chill.
Preheat oven to 325°.
Cut into ¼-in. slices; place 2 in. apart on ungreased baking sheets.
Prick with a fork.
Bake 10-12 minutes or until set.
Remove to wire racks to cool.
