Preheat oven to 375 degrees.

Lemon Filling:

1. Whisk together the egg yolks in a large 2 cup measuring cup or bowl and set aside.
2. Whisk together the water, cornstarch, sugar and salt in a medium saucepan. Bring mixture to a boil over medium heat, stirring constantly. Boil for 1 minute and remove from heat. Slowly pour about half of the hot mixture into the egg yolks while whisking constantly. This is called tempering. Whisk vigorously for about 1 minute. Add the mixture back to the pan and return to medium heat. Bring back to a boil over medium heat, stirring constantly and boil for 1 minute. Remove from heat. Add the butter, lemon juice, and lemon zest and mix well. Pour filling into pre-baked pie shell and set aside.  Click here  to see how to pre-bake a pie crust.

Meringue

Preheat oven to 300 degrees.

1. Place pie with filling in the oven while preparing the egg whites.  It’s important to place the meringue on hot pie filling.  The hot filling helps to cook the underneath of the meringue.
2. Place the egg whites, salt and cream of tartar in the bowl of a stand mixer fitted with the whisk attachment, or use a hand mixer.  Beat egg whites until soft peaks form and gradually add the sugar.  Beat until stiff peaks form.
3. Spread the meringue over the hot pie filling.  Spread meringue all the way to the edges of crust, ensuring that meringue touches the crust.  This keep the meringue from shrinking.  Use a spoon to make scallops or swirls in the meringue to your liking.
4. Turn oven to broil.  Place pie in the oven under the broiler.  Watch very closely.  Once the meringue starts to have patches of golden brown on top, immediately remove from oven.  This only takes a minute or two so watch carefully.
5. Allow pie to cool completely and refrigerate until pie is cold and firm enough to slice.