01 - Preheat oven to 350°F.
02 - Combine graham cracker crumbs, sugar, and melted butter in a medium bowl. Mix until evenly moistened.
03 - Press the mixture firmly into the bottom and up the sides of a 9-inch pie plate.
04 - Bake for 8 minutes. Remove from oven and set aside to cool while preparing the filling.
05 - Whisk together sugar, cornstarch, and salt in a medium saucepan. Gradually whisk in water until smooth.
06 - Cook over medium heat, stirring constantly, until mixture thickens and reaches a gentle boil, approximately 5 to 7 minutes.
07 - Remove from heat. Slowly whisk about 1/2 cup of the hot mixture into the beaten egg yolks, then whisk the warmed egg mixture back into the saucepan.
08 - Return to medium heat and cook, whisking constantly, for 2 additional minutes. Remove from heat and stir in lemon juice, lemon zest, and butter until fully incorporated and smooth.
09 - Pour the hot lemon filling into the cooled crust. Set aside.
10 - Beat egg whites and cream of tartar at high speed until soft peaks form.
11 - Gradually add sugar, 1 tablespoon at a time, beating continuously until stiff, glossy peaks form. Beat in vanilla extract.
12 - Spread meringue over the hot filling, ensuring it makes complete contact with the crust edges to prevent shrinking during baking.
13 - Bake for 15 to 18 minutes, or until the meringue is golden brown.
14 - Cool at room temperature for 1 hour, then refrigerate for at least 2 hours before slicing.