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 crumb mixture firmly into the bottom and up the sides of a 9-inch pie plate.
04 - Bake for 8 minutes. Remove from oven and let cool while preparing the filling.
05 - Whisk together sugar, cornstarch, and salt in a medium saucepan. Gradually whisk in water.
06 - Cook over medium heat, stirring constantly, until the mixture thickens and reaches a gentle boil, approximately 5-7 minutes.
07 - Remove from heat. Slowly whisk about 1/2 cup of the hot mixture into the beaten egg yolks, then whisk the warmed yolks 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, zest, and butter until smooth.
09 - Pour the hot 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 until stiff, glossy peaks form. Beat in vanilla extract.
12 - Spread meringue over the hot filling, ensuring it seals completely to the edge of the crust to prevent shrinking.
13 - Bake for 15-18 minutes, until the meringue is golden brown.
14 - Cool at room temperature for 1 hour, then refrigerate for at least 2 hours before slicing.