1. Put the butter and sugar in a large bowl and cream together until pale and fluffy.
2. Add the plain flour, rice flour and salt, and stir well until the mixture is smooth and uniform.
3. Bring the mixture together and press into a 20cm loose-bottomed sandwich cake tin, smoothing it with the back of a spoon. Crimp the edges by pressing with the tips of two fingers, or two knuckles. Then mark into 8 triangular pieces with a knife, and prick each triangle three times with a fork.
4. Put in the fridge for 30 minutes to firm up. Preheat the oven to 170°C, Gas Mark 3.
5. Remove the shortbread from the fridge and bake in the oven for 30–35 minutes, or until it is a very light golden colour.
6. Remove the shortbread from the oven and sprinkle over some caster sugar. Leave to cool in the tin for a few minutes before removing it from the tin and cooling on a wire rack. Once cold, cut into 8 pieces and serve.
7. For variety, add a tablespoon of grated stem ginger or the finely grated zest of 1 lemon or lime to the shortbread mixture.
Recipe courtesy of Lorraine Pascale, Baking Made Easy HarperCollins, 2012 (£20)