Shortbread can be made with plain flour alone, however the texture is greatly enhanced by using a combination of flours. Adding rice flour produces a light result, while semolina will give a crunchy texture.
Preheat the oven to moderate 180°C (350°F/Gas 4). Beat the butter in a wide bowl until smooth. Gradually beat in the sugar. Add the plain flour and rice flour or semolina and stir with a knife until well blended.