Place flour, salt and butter into a food processor and process until mixture looks like fine breadcrumbs and there are no lumps of butter. With the motor running, add a little water at a time until the dough just comes together.
Turn dough onto a cold surface. If you have a stone benchtop or a large marble or glass board, these are ideal. Gently knead dough a few times just to bring it together. Wrap in plastic wrap, refrigerate, 15 minutes.
Roll dough between two sheets of baking paper with a rolling pin. It needs to be done quite slowly and gently so that it is flattened, rather than stretched. Rest it again before using. If the dough is too soft it can be refrigerated on a tray. If it becomes too firm, stand at room temperature for a few minutes.