Sift cornflour, sugar and rice flour together in a medium-large bowl.
Add butter. Mix with hands until soft dough forms. If you feel that it's still too wet just add a little more flour (either one is fine). Refrigerate one hour.
Preheat oven to 150 C. Cover a baking tray with greased baking parchment. Shape dough into 2.5cm balls. Place about 5cm apart on greased parchment, then flatten with lightly floured fork. Bake for 20-25 minutes or until edges are lightly browned.