First, prepare all of your ingredients. Pre-bake a pie shell and let cool. Juice and zest lemons, separate your eggs, and measure out your other ingredients. Put your egg yolks in a small glass bowl and set aside.
Mix sugar and cornstarch in a pan. Then, add water. Bring mixture to a boil, stirring constantly. Boil for 1 minute and then remove from heat.
Add part of your mixture to the bowl with egg yolks, one spoonful at a time and stirring as you pour. Once you have about 1/3-1/2 of the mixture stirred in with the egg yolks, add the egg yolk mixture back into the pot. Stir until mixed through.
Bring your mixture back back to a boil and boil for one more minute, stirring constantly. Then, turn off heat and add lemon zest, juice and butter. Mix until incorporated.
Pour your filling into a cooled pie shell. Make your meringue.
Meringue
In a cold mixing bowl, beat egg whites and cream of tartar on high speed in a kitchen aid or with a hand mixer until frothy.
Add sugar, 1 T at a time. Beat until stiff peaks form.
Add vanilla.
Spread over pie, forming peaks with the end of your spoon.
Bake at 400 degrees for 6-8 mins.
Let your pie cool to room temperature before refrigerating, then refrigerate for a couple of hours before serving.
