Line a baking tin with greased paper. Sieve the flour. Add the rice flour and sugar. Knead in the margarine. When the mixture binds, pack it into the tin. Prick the top with a fork and crimp the edges with your thumb.

Bake at the bottom of the oven at GM 3 / 325 °F / 170 °C until firm and lightly browned (About 1 hour.)

Move onto a wire cooling tray and drench the top with caster sugar.