Make the pastry following the flaky pie dough recipe here. On a lightly floured worksurface, roll out one of the discs into a circle 2-3mm thick and 5cm wider than the pie tin. Roll the pastry onto the rolling pin and carefully drape into the pie tin, trimming the excess so that there is an overhang of about 2.5cm. Roll up the overhang into a sausage sitting around the pie plate and, using the thumb and forefinger of one hand and the forefinger of the other, crimp the pie every 5cm, and chill until the pastry is firm. Prick the base all over with a fork, line with a crumpled sheet of baking paper and fill with baking beans or rice. Brush the crimped edge of the pie with the beaten egg and sprinkle with a little demerara sugar. Bake for 20 minutes before removing the baking beans and baking for a further 10 minutes until the base is turning a light golden brown. Brush the inside of the pie with more beaten egg, coating the entire base, and bake for another 2 minutes. This helps prevent a soggy base with wet fillings.