Butter a 9 inch round cake tin, line with baking parchment then butter again.
Place all the ingredients except the butter into a food processor and pulse until all mixed together.
Add in the butter and pulse again until the mixture resembles wet sand.
Press the mixture into the cake tin until flat. I like to use the back of a flat measuring cup to do this.
If you want the classic shortbread finish then using a fork, prick the shortbread working in lines until you have a neat pattern.Place in the freezer for 30 minutes whilst you heat the oven to 180ºC. Bake for around 30 minutes.
Once removed from the oven, I like to go over my fork marks by gently pricking the shortbread again. Whilst still warm, use the end of a wooden spoon to make an indent all around the edge of the shortbread.Again whilst still warm, using a long knife, score where the shortbread will be cut into slices. Cool in the tin for 10-15 minutes then remove and leave to cool on a wire cooling rack.