Preheat oven to 325 degrees F (165 degrees C).

Line a baking sheet with greaseproof (parchment) paper. Sift the flour and rice flour into a medium mixing bowl. Add the sugar and mix.

Cut butter into pieces and rub into the flour with your fingertips until the mixture begins to bind together. Knead into soft dough.

Roll the dough into an 8 inch round (or for exact round, mold it in an 8 inch cake pan). Place on baking sheet. Using a fork, prick top and make tine marks along edge. Using a table knife, score top with wedge marks. (This is where it will break when cooled)

Bake 45 minutes or until pale golden in color. Sprinkle a little superfine sugar over top and cool on baking sheet. Cut into wedges. Keeps for weeks in airtight tin.