Cut the cold butter into small cubes.
In a bowl, add the flour, icing sugar, and cold, cubed butter. Using your fingertips, rub the butter into the flour until the mix resembles breadcrumbs. Add a dash of milk and bring the mix together into a dough. Don't knead it; just bring it together until combined. Avoid overworking the dough, as this develops the gluten.
Transfer the dough to a work surface, flatten it into a disc, wrap it in parchment paper, and refrigerate for 1 hour.
After resting, remove the dough from the fridge and set it aside for 5 minutes.
Lightly flour the work surface and roll the dough into a disc larger than the tart tin. The disc must be larger than the tart tin's diameter. Measure the diameter of the tin base, add the tin depth, and add approx. 2.5 cm (1 inch) to that. The disc should be no thicker than 3mm.
Carefully line your tart tin with pastry, gently pressing it to match the tin's shape. Try not to stretch the pastry, and patch any cracks that might appear. Trim the overhanging pastry with a knife.
Preheat the oven to 180ºC (fan-assisted)
Prick the pastry base with a fork to prevent it from rising. Refrigerate for at least 15 minutes.
Line your pastry case with baking parchment and fill with ceramic baking beans, uncooked rice or dried beans.
Bake for 15 minutes, then remove from the oven, take out the parchment and beans, and bake for a further 5 minutes.
Once done, remove from the oven, and leave to cool in the tin.