- Preheat the oven to 375°F and grease a 9 inch square pan.
- Beat the butter for 2 minutes, to make it fluffy and light. Add the icing sugar and sugar and beat again for 2 minutes until fluffy. Beat in the vanilla, then add the flour, rice flour and salt, stirring until evenly blended.
- Scrape the dough into the prepared pan and press it flat into the bottom of the pan (the dough is quite firm and easy to press, but if your fingers do stick, dust them with a little flour). Use a fork to dock the shortbread at 1 inch intervals, then bake for about 25 minutes until the outside edges of the shortbread have browned a little. Let the shortbread cool for 10 minutes, then cut the shortbread into squares. Let the cookies cool completely before lifting them out of the pan to store.
The shortbread will keep in an airtight container for up to a week.