Start by making the lemon curd.  In a medium bowl, whisk the eggs yolks until they are smooth and creamy.  Set aside.

In a saucepan over medium heat, combine the cornstarch, sugar, salt, and water.  Whisk to combine until smooth. Cook, stirring constantly until the mixture comes up to a boil.  Cook, while stirring, for another minute or two or until the mixture begins to thicken. It should be a very thick pudding consistency.

Remove the pan from the heat.  Use a tablespoon, scoop one spoon of the hot cornstarch mixture and quickly whisk it into the beaten egg yolks.  This is called tempering the eggs. Continue to whisk in spoonfuls of the cornstarch mixture until you use half of the cornstarch mixture.

Add the tempered egg yolk mixture into the saucepan of cornstarch.  Return to a boil over medium-low heat, stirring constantly – about 3 to 4 minutes.

Remove the pan from the heat.  Whisk in the lemon juice, zest, vanilla, and butter.  Set aside.

Preheat the oven to 325 degrees.

Prepare the meringue.  In a small saucepan over medium heat, combine the cornstarch and water.  Stir until the mixture just comes to a boil and begins to thicken. Remove from the heat and set aside to cool.

In a small bowl, stir together the sugar and cream of tartar.  Set aside.

In the bowl of an electric mixer, slowly start whipping the egg whites and vanilla together until the egg whites become frothy.

Slowly add in the sugar and cream of tartar mixture, one spoon at a time.  Continue beating the egg whites until soft peaks form.

While continuing to beat the egg whites, spoon in the cornstarch mixture.  Increase the mixer speed to high and beat until the egg whites form stiff peaks.  Be careful not to overbeat the egg whites or they will feel grainy.

Next, fill the baked pie shell.  Gently re-warm the filling over medium heat, stirring constantly until hot and pourable.  Pour the hot filling into the crust and smooth the top.

Top the pie with meringue.  While the filling is still hot, use a rubber spatula to spread the meringue mixture on the pie, making sure that the meringue makes contact with the crust all the way around the pie.  This will anchor the meringue so it doesn’t shrink.

Scoop the last of the meringue into the middle of the pie to make a small slope.  Use the back of a spoon to make peaks and swirls in the meringue.

Bake the pie for 20 minutes at 325 degrees until the meringue is golden brown.

Remove the pie from the oven and cool on a wire rack until room temperature.  Once room temperature, chill for at least an hour to help firm the filling.

The pie will last for 2 days covered in the refrigerator, however, it is best eaten the first day.