Put flour and butter into a bowl and either rub the butter into the flour, or mix it in the food processor until it is a breadcrumb consistency. Make sure that all the lumps of butter are rubbed in.
Add a couple of pinches of salt and caster sugar, and mix with the breadcrumb consistency ingredients.
Add a little water at a time and either mix by hand, or in the mixer / processor until the dough forms a ball. Stop when the dough has bound together. I add a tablespoon at a time until the ball begins to form.
Wrap the dough up with cling film and refrigerate for approximately half an hour before using it.