Using a food processor, cut the butter into the flour and salt until the mixture is crumbly, then incorporate the water and lemon juice by hand just until you have a smooth dough. Roll into a ball, wrap it in plastic wrap and refrigerate for 1 hour.
Shaping and Blind Baking
Preheat the oven to 170°C (325°F/Gas 3). If the pastry dough is too hard when it comes out of the refrigerator, let it soften. Butter and flour a 26 cm (10½ inch) pie dish. On a floured surface, roll out the dough into a round large enough to hang over the edge of the dish by about 3 cm (1¼ inches). Place the round of dough in the dish, then roll the overhang onto itself and pinch with your fingers to shape the edge. Cover the pastry with baking paper and dried beans and bake for about 40 minutes until the edges are golden and the pastry is quite dry. Remove the paper and beans and brush the base with the beaten egg. Return to the oven for 2 minutes until dry and light golden.
Preheat the oven to 180°C (350°F/Gas 4). Whisk together the eggs, egg yolk and sugar. Incorporate the rest of the filling ingredients one by one and mix until combined. Pour the filling into the pastry shell and bake for about 40 minutes until the filling has set. Allow to cool before serving.