Step 1

Preheat oven to 325 degrees.

Step 2

In a medium sized saucepan combine 1 1/3 cup sugar, and 1/3 cup cornstarch, until well combined. Slowly stir in milk, lemon juice, and 1/2 cup water to prevent lumps.

Step 3

Add lemon zest, and bring to a boil. Stir while cooking, until mixture starts to thicken.

Step 4

Whisk 1/4 cup at a time of lemon mixture into egg yolks, until 1 cup of lemon mixture has been added. Add egg yolk mixture back into lemon mixture. Stir while returning to a boil. Cook an additional 1-2 minutes, until mixture is thickened. Remove from heat. Whisk in butter, and vanilla.

Step 5

Pour mixture into baked pie crust, and set aside.

Step 6

In a small saucepan combine 1 tablespoon cornstarch, and 1 tablespoon sugar, until well combined. Slowly pour in 1/3 cup water to prevent lumps. Cook over medium heat, and bring to a boil. Cook for 20 seconds once boiling. Remove from heat to cool.

Step 7

Beat egg whites, cream of tartar, and vanilla together, until soft peaks form.

Step 8

Slowly add 1/2 cup sugar while beating. Beat until stiff peaks form, and mixture becomes glossy.

Step 9

On low speed mix in 1 tablespoon of cooked cornstarch mixture at a time, until all cornstarch mixture is incorporated. Mix until well combined.

Step 10

Mound meringue mixture over pie, and anchor into the edge of pie crust to prevent shrinking. Use the back of spoon to form small peaks all over pie.

Step 11

Bake in preheated oven for 18-25 minutes, until lightly brown on top.

Step 12

Cool pie completely before slicing, or refrigerate for 6 hours, or until cold for best flavor before slicing.