01 - Preheat oven to 350°F. Combine graham cracker crumbs, sugar, melted butter, and salt. Press firmly into bottom and up sides of a 9-inch pie dish. Bake 8 to 10 minutes until set and lightly golden. Remove and let cool.
02 - Whisk sugar, cornstarch, and salt in a saucepan. Gradually stir in water, lemon juice, and zest. Cook over medium heat, stirring constantly, until mixture thickens and boils. Boil for 1 minute more.
03 - Whisk egg yolks in a small bowl. Gradually whisk in about 1/2 cup hot lemon mixture. Return mixture to saucepan and cook, stirring, for 2 minutes. Remove from heat and stir in butter until melted. Pour filling into cooled crust.
04 - Beat egg whites and cream of tartar with an electric mixer on medium speed until soft peaks form. Gradually add sugar, one tablespoon at a time, beating to stiff, glossy peaks. Beat in vanilla extract.
05 - Spread meringue over hot lemon filling, sealing edges to crust. Bake at 350°F for 15 to 18 minutes until meringue is golden brown.
06 - Let cool at room temperature for 1 hour, then refrigerate at least 2 hours before serving.