1/2 cup butter or margarine -- softened
1/2 cup shortening
1/2 cup packed brown sugar
1/4 cup granulated sugar
2 1/4 cups all-purpose flour
1 teaspoon salt
Heat oven to 300∫. Beat butter, shortening and sugars in large bowl with electric mixer on medium speed, or mix with spoon. Stir in flour and salt. (Dough will be dry and crumbly; use hands to mix completely.)
Roll dough into rectangle, 15 ◊ 7 1/2 inches, on lightly floured surface.
Cut into 1 1/2-inch squares. Place about 1 inch apart on ungreased cookie sheet. Bake about 25 minutes or until set. (These cookies brown very little, and the shape does not change.) Remove from cookie sheet to wire rack.