Cream butter and suagr until light and fluffy.
Add all other ingredients and mix well.
On a lightly floured surface, roll out the dough until you have a long round log.
Cut the log in half, and form each round log into an angular rod shape. Wrap each log in plastic and refrigerate for about an hour until the logs are hard.
Whe you're ready to bake the shortbread, preheat the oven to 160°C (140°C fan-forced) and remove the dough from the fridge.
Cut the logs into thin slices, about 1 cm in thickness.
Place cut dough onto baking trays lined with baking paper. They will spread out a bit, so give them a bit of space.
Bake for 20-25 minutes until golden brown (they will be slightly soft to touch). They will continue to cook a little once you remove them from the oven, and then harden once cooled.
Store in an airtight container for up to 5 days.