Sift the flour into a large bowl, add the butter and rub in with your fingertips until the mixture resembles fine breadcrumbs.
Stir in the salt, then add 2-3 tbsp water and mix to a firm dough. Knead the dough briefly and gently on a floured surface. Wrap in cling film and chill while preparing the filling.
To make more or less, remember the proportions - half fat to flour - and don't add too much water or the pastry will be hard. For best results, make sure the butter is cold. If other dry ingredients are included in the recipe, add them at the same time as the salt.