Put the flour, butter and salt in a bowl, and rub with fingers until the mixture resembles breadcrumbs.
Add small amounts of cold water, gently mixing until the mixture just comes together. You do not want the mixture to end up too wet so add the water in very small amounts at a time.
Wrap the pastry in cling film and chill in the refrigerator for 20 minutes.
When the pastry is chilled, pre-heat your oven to 200˚C. Roll the pastry out on a lightly floured surface until large enough to fit your 12" Flan tin, ensuring you have rolled it out enough to fill the bottom and sides of the tin. Gently push the pastry into the sides of the tin, and remove excess pastry from around the top.
Using a fork, prick the bottom of the pastry in several places, then cover with grease proof paper and add ceramic baking beans. Place in the oven and blind bake for 15 minutes.
Remove the baking beaks and grease proof paper, and return to the over for a further 5 minutes.