Caramel Macadamia Shortbread

250 grams butter -- chopped

1/2 cup brown sugar

1/2 cup icing sugar mixture

1 1/2 cups plain flour

1/3 cup rice flour

1/3 cup cornflour

2/3 cup chopped macadamia nuts

1 tablespoon sugar

Grease 20cm x 30cm lamington pan. Beat butter and sifted brown sugar and icing sugar in small bow lwith electric mixer until smooth. transfer mixture to large bowl, stir in sifted flours and nuts. press mixture into prepared pan, mark into 25 rectangles with sharp knife, sprinkle with white sugar. Bake in moderately slow oven about 40 minutes or until lightly browned, cool in pan.