Grease 20 cm round cake pan. Line bottom with wax paper. In bowl, cream butter until fluffy. Mix in all purpose and rice flours, and white and brown sugar with electric beater until dough is crumbly but clumps together when pressed. Pat evenly into prepared pan. Bake in preheated 180ºC oven 45 minutes. Remove from oven briefly, with sharp knife, score into dozen wedges, cutting about halfway through dough. Price decoratively with fork. Return to oven; bake about 15 minutes longer or until just lightly browned at edges. Cool in pan on rack 30 minutes. Loosen sides;invert again on cooling rack so cookie is right side up. Cool completely. MAKES: dozen large wedges