Pre-heat the oven to 300ºF. Butter a 9-inch square cake pan and then line it with parchment paper, leaving flaps of parchment paper to hang over the sides of the pan (this will make it easy to remove the shortbread). Butter the parchment paper too.

Using a food processor or mini chopped, process the sugar until it becomes superfine sugar – pulse it for about 30 seconds.

Blend the butter and sugar together in a stand mixer with the paddle attachment or in a bowl with a wooden spoon. Add the flour and salt and blend just until the ingredients are combined into chunks and no dry flour is visible.

Transfer the mixture to the buttered cake pan and press the dough into the pan, using your hands, a spatula or a drinking glass to smooth it out at the end.

Chill the dough in the refrigerator for at least 15 minutes or longer. Dust the top of the shortbread with more superfine sugar and then transfer to the oven and bake for 45 minutes or until very lightly golden brown around the edges of the pan.

Remove the shortbread from the oven and let it set up for 10 minutes or so. Then, cut the shortbread into the desired serving sizes.The cookies will be tender, but will get crispier over time. Store in an air-tight container for up to 3 weeks.

*To make flavored shortbread, add any optional ingredient to the butter and sugar and combine before adding the flour.