Line 9-inch square pan with foil, extending foil over edges of pan; butter foil. Cover bottom of prepared pan with chocolate chips.
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.
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. About 1-1/2 pounds candy.