Traditional Scottish shortbread

Set the oven to 160C/gas 2.

Place all the ingredients together in a food processor and whizz until the mixture forms a smooth dough (if preferred this can be done by hand in a bowl using soft butter).

Roll the shortbread out to form a circle with a 20cm diameter and flute the edge (alternatively, press into a 20cm loose bottomed cake tin).

Prick gently over the top with a fork and score the surface of the round into 8 even wedges. Sprinkle with caster sugar. Bake for 20-25 minutes until firm and golden.

Set aside to cool a little, but cut into wedges while still slightly warm. Store in an airtight tin.