Combine the cold butter, flour, salt and sugar in a food processor. Pulse in short bursts with a couple of seconds breaks between each burst. The key is to keep the butter cold, long bursts will create heat by friction and melt the butter. Once lightly combined add the vodka and pulse 2-3 more times. Last add the ice cold water. Careful don't add too much, go one table spoon at a time. The texture should stay crumbly and NOT become a batter or dough.
Place the crumbly dough on your working surface and lightly knead together. Don't forget the dough must stay cool so wash your hands with cold water before you start. Knead the dough together very very lightly. Its almost like we are just compacting it in to a ball. Now wrap with kitchen membrane and place in the fridge for 30-40 minutes until the butter sets again.
Now that the dough has cooled, we can roll it in to a sheet. Our pie dish is 9 inches in diameter and as we need to cover the sides and lip we will roll the dough out to 11+ Inches. Very lightly flour your working surface and roll the dough out evenly in all directions. The edges will sometimes crack and that's ok, just pinch them back together. If you feel the dough is starting to melt or get soft. Pop it back in the fridge for a few minutes and then continue.
Now roll the dough up on your rolling pin (all lightly floured to avoid sticking) and carefully release it on the pie form. Lightly push it in to the corners and overlap evenly around the lip. Using a knife trim the edges just under the lip. The pie dough needs an edge to hold onto otherwise it will collapse in to the pie dish. Now fill with your baking weights for blind baking and half bake for 20-25 minutes.
Lemon Pie Filling
Separate the egg yolks from the egg white. Set the egg white aside as you will need it for the meringue. In a medium sized saucepan combine the water, sugar, cornstarch, salt and lemon zest. Set to medium heat and constantly stir until the sauce thickens. Don't let it boil. Once thickened add 3-4 table spoons of the thick sauce in to the egg yolks while constantly whisking. This will temper the eggs and avoid clotting. Now add the tempered egg yolks back in to the sauce pan and stir until smooth. Add in the butter and lemon juice and whisk until combined. Pour in to the baked pie shell and set aside to cool.
In a medium sized saucepan combine the water, corn-starch and 2 tbsp of sugar. Set over a medium heat until the sugar and water are combined in to a foggy mixture. As soon as it starts to thicken set aside. In a mixing bowl, combine the egg whites, salt, vanilla extract and remaining sugar and whisk with an electric mixer to soft peaks. Add in the cooled corn-starch mixture and beat to stiff peaks. Place evenly on the lemon pie and place in the oven at 175C for 20 to 25 minutes until fully baked and the meringue has set. Allow to cool for at least 3-4 hours then serve.