01 - Preheat oven to 350°F (175°C).
02 - In a medium bowl, combine graham cracker crumbs, sugar, and melted butter. Mix until evenly moistened and crumbly.
03 - Press the mixture firmly into the bottom and up the sides of a 9-inch pie plate, creating an even layer.
04 - Bake crust for 8 minutes until lightly set. Remove from oven and allow to cool while preparing the filling.
05 - In a medium saucepan, whisk together sugar, cornstarch, and salt. Gradually whisk in water until smooth.
06 - Cook over medium heat, stirring constantly, until mixture thickens and comes to a gentle boil, about 5-7 minutes.
07 - Remove from heat. Slowly whisk about 1/2 cup of hot mixture into 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 until thickened. Remove from heat.
09 - Stir in lemon juice, lemon zest, and butter until completely smooth and incorporated.
10 - Pour hot lemon filling into the cooled pie crust. Set aside while preparing meringue.
11 - Beat egg whites and cream of tartar at high speed until soft peaks form.
12 - Gradually add sugar, 1 tablespoon at a time, beating continuously until stiff, glossy peaks form.
13 - Beat in vanilla extract until fully incorporated.
14 - Spread meringue over hot filling, ensuring it completely covers the filling and seals to the crust edges to prevent shrinking.
15 - Bake for 15-18 minutes until meringue is golden brown on peaks.
16 - Cool pie at room temperature for 1 hour, then refrigerate for at least 2 hours before slicing and serving.