To make the pastry, sift the flour, salt and sugar together into a bowl. Cut the butter into small pieces and rub into the flour until the mixture resembles coarse breadcrumbs. Using a fork, mix in the egg and just enough water to bind the dough together. Shape the dough into 2 discs, one larger than the other. Wrap in cling-film and refrigerate while you prepare the filling.
Place a ba