Line two baking trays with baking parchment. Ensure your butter is very cold. Cut the butter into cubes.

Sift the flour, sugars and salt together in a large bowl and mix to combine. Add the cold butter and use your fingertips and thumbs to rub the flour mix into the butter until it resembles fine breadcrumbs. Add the egg yolk and vanilla and use your hands to gently bring the mixture together into a dough, being careful not to overwork it.

Using a rolling pin, roll the dough out on a floured surface to approximately 1cm thick. Use an 8cm cookie cutter (or 6cm if you prefer mini shortbreads) to cut the dough into circles. Place them on the prepared baking tray and refrigerate for a minimum of 2 hours, but preferably overnight.

Heat the oven to 180°C fan.

Slide the baking tray into the oven and bake for approximately 12 mins, or until the edges are just starting to brown. Remove from the oven, cool on the tray for a couple of mins, then transfer to a wire rack. Dust the tops with more sugar and leave to cool completely.