Put the sugar in a bowl (reserving 2 tbsp for later) and add the finely grated lemon zest. Rub together with your hands to help release the lemon oils.
Add the flour and cold, cubed butter and rub together until you have an even crumb.
Add 1 tbsp of cold water and cut through with a cutlery knife. Give a little bit of the mixture a squeeze. If it comes together, it’s ready. If it’s dry and sandy, cut in up to another 1 tbsp water.
Gather up the pieces and knead together only as much as it takes to get a smooth ball of dough.
Roll the dough into a cylinder with a length of 25cm and a diameter of 4cm. Wrap in greaseproof paper or plastic wrap and place in the fridge to rest and chill for 15 minutes.
While the dough chills, preheat the oven to 170C (150C fan / 340F).
Slice the dough into 1 cm cookies.
Place them on a lined baking tray and prick each one a few times with a fork.
Bake for 20-25 minutes until they've taken on just a very slight golden colour.
As soon as they’re out of the oven, sprinkle with the reserved sugar and allow to cool for 5 minutes. Transfer to a wire rack to cool completely.