Because this is my mom's lemon pie recipe, there are only a couple of rules to be followed here. The lack of rules can make this more complicated than it has to, but don't let that happen. If you are looking for a recipe that doesn't require much precision, one to have fun tweaking and improving, this is it.
Just try to enjoy the freedom of the recipe. Use your judgment on quantities (the dough may require extra flour).
Crust
200 grams of all-purpose flour
100 grams of unsalted butter at room temperature
1 tablespoon of sugar
1 egg yolk
2 eggs
1 lemon's zest
A splash of vanilla extract
Filling
3 eggs (1 full, 2 yolks)
100 grams of sugar
1/4 cup of cornstarch (you can use 2 tablespoons of flour if you don't have cornstarch)
3 lemons
Italian Meringue
3 egg whites
210 grams of sugar
Make the crust: mix the butter and sugar until well combined. Add the 2 eggs, 1 egg yolk, lemon zest, and vanilla extract. Add the flour until you form a dough. Don't knead it and try to touch it as little as possible. Seal with plastic wrap and refrigerate. You can always make the dough 1-2 days ahead.
For the filling, whisk 2 yolks and a full egg (or 3 yolks, up to you) with the sugar. I usually whisk this in the same pot I'll use to make the filling. Add the zest of three lemons and squeeze the juice of 2 of those. Combine well.
Separately, dissolve the cornstarch in water (around 1/2 liter).
Place the pot with the filling on medium heat and stir. Slowly add the dissolved cornstarch. Stir from time to time, making sure that it doesn't stick to the bottom and that the mixture is homogeneous. Let it thicken, remove from the heat, and stir in the butter until it combines well.
Roll and bake the dough in a 350°F oven. Let it cool for a bit (5-10 minutes) while you start on the meringue, and then pour the filling on the crust.
Make the Italian meringue by following these steps. When it's ready, top your lemon pie with it.