Juice of 4 lemons (you need 150ml lemon juice - Tip - to obtain more juice from your lemons, place them into a microwave dish and microwave for 30 seconds)
Sift dry ingredients into food processor and add butter. If you haven't got a processor use a mixing bowl.
Process briefly until blended in the processor or rub together the ingredients by hand until they look like breadcrumbs.
Mix together egg yolk and water and add this mixture slowly through the feeder tube of the processor and when pastry comes together, gather into a ball, wrap in clingfilm and refrigerate for an hour. If you don't have a processor add the mixed egg yolk and water to the mixing bowl and using a palette knife cut, mix and finally bring together the ingredients by hand until they can be gathered into a ball (you may want to do this on a floured board). Once rolled into a ball, wrap in clingfilm and refrigerate for an hour.
Lightly butter a 9 inch flan dish (preferably with a loose bottom) and sprinkle flour carefully over the buttered flan dish and set to one side
Roll out the dough to fit the flan dish, ensuring it can come up over the edge of the dish and then carefully roll the dough over your rolling pin and gently place the rolled out dough into the flan dish, gently pushing it down into the edges of the dish and leaving the edges to overhang.
Prick the dough with a fork (you are trying to prevent the dough rising as its cooking but don't prick to far down into the dough otherwise you will create holes!)
Cover (loosely) the flan dish with cling film and place on a baking sheet in the fridge for at least 2 hours or, preferably, overnight. I now prefer to get this point and then finish off the rest of the recipe the next day.
Preheat the oven to gas mark 4.
Take out the flan dish from the fridge (still on its baking tray) and carefully remove the clingfilm.
Cut up some baking paper (at least a half a size larger than the flan dish) and scrunch up in your hands. Repeat with another piece of baking paper. Place one piece carefully into the flan dish (half way) and repeat with the other piece covering the other half.
Scatter a box of baking beans over the scrunched up paper ensuring they cover the bottom of the dish.
Carefully tuck the baking paper under the flan dish so that no dough is exposed. It should remain on the baking tray as the baking tray with the flan dish will both be going into the oven.
Place the baking tray and prepared flan dish into the oven and blind bake for 20 minutes
Remove from the oven and carefully lift the baking paper and beans out of the flan dish.
Very carefully roll a rolling pin over the top of the blind baked pastry case and the rolling pin will miraculously cut the edge of the pastry leaving a nice clean edge (thanks canteen ladies!).
Mix an egg white with a fork until frothy.
With a pastry brush, lightly brush the bottom of the pastry case with the frothy egg white and return to the oven for another 20-25 minutes until light golden brown.
While the pastry case is cooking, break the eggs for the filling into a large bowl and whisk together with a wire whisk.
Add the rest of the filling ingredients and whisk until well combined.
Transfer the mixture to a pouring jug.
Once the pastry is light golden brown, remove from the oven and allow to cool
Turn down the oven to gas mark 3.
Once cool, place the pastry case (still on the baking tray) onto an oven shelve and carefully pour the filling into the pastry case.
Cook for 20-25 minutes until the filling has set but still has a slight wobble in the middle.
Remove from the oven and allow to cool.
A tip for removing flans from flan cases - place the flan case on top of a can and the flan case will drop away.
Recipe by Doe's Kitchen at http://doeskitchen.com/tarte-au-citron-or-lemon-tart/