1. Line 9-inch square pan with foil, extending foil over edges of pan; butter foil. Cover bottom of prepared pan with chocolate chips. 2. Combine cashews, macadamia nuts, butter, sugar, and corn syrup in large heavy skillet; cook over low heat, stirring constantly, until butter is melted and sugar is dissolved. Increase heat to medium; cook, stirring constantly, until mixture begins to cling together and turns golden brown. 3. Pour mixture over chocolate chips in pan, spreading evenly. Cool. Refrigerate until chocolate is firm. Remove from pan; peel off foil. Break into pieces. Store tightly covered in cool, dry place.