Sift the flour and place it in a big bowl. Sitr in the sugar and salt.
Add in the cold butter and make a sand-like mix using a fork. It is important not to overdo this step, it has to be quick so that the butter stays cold.
Then add in the egg yolks and vanilla. Incorporate well until you get a soft dough (you can also do all this using a food processor following the same steps).
Wrap the dough in plastic wrap and leave it in the fridge for 30 min.
Once the 30 min. have passed, roll out the dough in a previously floured surface to be 3 mm thick.
Place the dough in a pie mold, cut the excess and pinch a little with a fork.
Cover the dough with parchment paper or aluminium foil and put on top something to make some weight. You can use uncooked rice, beans, etc.
Bake at 350°F for 20 min. or until fully cooked.
Let it cool completely before filling.
For the filling:
On a pot to medium heat, heat the milk with half the sugar.
In a different bowl, mix the rest of the sugar and corn starch together. Incorporate the egg yolks, lemon juice and zest and salt. Once mixed, add in some warm milk to temper the mixture.
Cook it in the pot with the rest of the milk, always stiring.
Cook until it boils for a minute and then turn off the heat.
Add in the butter, mix and then cover it with plastic wrap, making sure the plastic wrap touches the mixture so that it doesn´t form a custard on the surface.
Once this mmixture has cooled down, fill with it the pie crust.
Take the pie to the fridge for 1 hour until the filling is thick in consistency.
For the meringue:
In a small pot to low heat, heat the water and sugar together, until the mixture gets to 239° F (you can test this by dropping a little of this mixture in a glass with cold water, if a soft ball forms while touching it with your fingers, it´s ready). Once it´s ready turn off the heat.
In the meantime, in a standing mixer, beat the egg whites along with the cream of tartar and the lemon juice to medium speed for 2 min.
While still beating (now to high speed), slowly pour the hot sugar syrup and keep beating until stif peaks form.
Once the meringue is firm and shinny, it´s done! now you can spread it on top of the pie.
Finaly, you can use your oven grill or a kitchen torch to golden the meringue.