Beat the butter and sugar together in a mixing bowl or a food processor until pale and creamy. Sift in the flour, rice flour and salt and mix or process briefly until the ingredients just come together.
Transfer to a work surface and knead lightly to form a soft dough. Shape into a disc, wrap in clingfilm and chill for 30 minutes.
Divide the dough in half and roll out each piece on a lightly floured surface to a 20 cm (8 inch) round. Transfer to 2 ungreased baking sheets. Score each round with a sharp knife, marking it into 8 equal wedges, prick with a fork and use your fingers to flute the edges.
Sprinkle over a little caster sugar and bake in a preheated oven, 190°C (375°F), Gas Mark 5, for 18–20 minutes until golden. Remove from the oven and, while still hot, cut into wedges through the score marks. Leave to cool on the baking sheet for 5 minutes then transfer to a wire rack to cool. Store in an airtight tin.