Mix the butter, icing sugar, salt and vanilla extract using an electric mixer or a whisk until it's nice and fluffy. Remember to use a spatula to scrape down the sides and bottom every once in a while if using a stand mixer.
Mix in the flour using a spatula.
Roll it to 5mm in between two sheets of baking paper. Chill for 1-2 hours or until firm.
Remove from the fridge and cut into 2x5cm rectangles. Place them onto a baking tray lined with baking paper or a silicone mat. Use a skewer to poke small holes on the surface. Sprinkle with granulated sugar.
Bake in a preheated oven at 180℃/350℉ for 12-15 minutes or until lightly golden