Finely chop the macadamia nuts. Sift flour, sugar and cornstarch. Stir in nuts. Beat butter in bowl at medium speed until creamy. At low speed, beat in flour mixture. Using a level tablespoon, shape dough into balls. Place 2 inches apart on ungreased baking sheets. Flatten each ball with a fork. Bake in preheated 300 degree oven 25 to 30 minutes until just lightly browned around edges. Cool baking sheet on rack 5 minutes. Transfer cookies to rack to cool. Variations: Press half a macadamia nut into each cookie before baking. Sprinkle with rock sugar upon removing cookies from oven. From Family Circle's "Our Best-ever Cookie Collection". ----