For 'gritty' granulated texture:

125g plain flour
25g rice flour
100g butter
50g caster sugar

For a fine but crunchy texture:

100g plain flour
25g rice flour
25g cornflour
100g butter
25g caster sugar
25g icing sugar

For a smooth 'melting' texture:

100g plain flour
50g cornflour
100g butter
50g icing sugar

Put the butter on to a work surface and knead in the sugar, then the flour until it becomes a reasonably firm ball of dough. (to make in a food processor pulse butter and sugar till creamy, add flour and pulse until smooth. Remove and knead, adding more flour if needed.)

Either press dough into a greased 270x175mm swiss rool tin and prick with a fork, or use a special shortbread mould, or roll into a cylinder shape and coat in granulated sugar. Chill and slice into thin round biscuit shapes. Bake slowly at 170C until an even golden brown.