Combine the dry and butter.
In a food processor, add the flour, salt, and sugar (if using) and pulse briefly.
Add the cold, cubed butter and pulse until the mixture resembles fine breadcrumbs. Alternatively, do this by hand in a large bowl, rubbing the butter into the flour with your fingertips.
Add the ice-cold water. With the food processor running, slowly pour the water down the funnel until the dough just comes together into a ball. If mixing by hand, use a butter knife to stir the water in a little at a time. Be careful not to add too much water at once – you may not need it all.
Form the dough. As soon as the dough forms, stop mixing. Overworking the dough will develop the gluten and result in a tough pastry. Gently bring it together with your hands into a smooth disc.
Roll out the pastry.
Place the dough between two large sheets of baking parchment.
Using a rolling pin, roll it out to an even thickness of about 2mm (just under 1/8 inch). This method prevents the dough from sticking without adding extra flour, keeping it perfectly buttery.
Use or store. You can use the pastry immediately, or store it for later. To store, keep it flat between the parchment sheets on a tray, cover tightly with cling film, and refrigerate for up to 5 days.
Roll the pastry between two sheets of baking parchment. This is the secret to a moist, buttery dough as you don't need any extra bench flour, which can dry it out.