01 - Preheat the oven to 350°F.
02 - In a bowl, combine graham cracker crumbs, sugar, melted butter, and salt until well mixed.
03 - Press the mixture firmly into the bottom and up the sides of a 9-inch pie dish and bake for 8 to 10 minutes until set and lightly golden. Remove and allow to cool.
04 - Whisk together sugar, cornstarch, and salt in a saucepan. Gradually incorporate water, lemon juice, and zest while whisking continuously.
05 - Place over medium heat and stir constantly until thickened and boiling. Continue cooking for 1 more minute.
06 - In a small bowl, whisk egg yolks. Gradually add about 1/2 cup of the hot lemon mixture to the yolks to temper, then return all to the saucepan.
07 - Cook, stirring for 2 additional minutes. Remove from heat and stir in butter until fully melted. Pour the filling into the cooled crust.
08 - Using an electric mixer, beat egg whites and cream of tartar on medium speed until soft peaks form. Gradually add sugar one tablespoon at a time, beating until stiff, glossy peaks develop. Stir in vanilla extract.
09 - Spread meringue evenly over hot lemon filling, ensuring it seals to the crust edges to prevent shrinking.
10 - Bake at 350°F for 15 to 18 minutes until meringue is golden brown.
11 - Cool at room temperature for 1 hour, then refrigerate for at least 2 hours before slicing.