01 - Preheat oven to 350°F. In a mixing bowl, combine graham cracker crumbs, sugar, and melted butter until evenly moistened. Press the mixture firmly into the bottom and up the sides of a 9-inch pie pan to form an even crust.
02 - Bake the crust for 8 minutes until set and lightly fragrant. Remove from the oven and set aside to cool while preparing the filling.
03 - In a medium saucepan, whisk together sugar, cornstarch, salt, and lemon zest until combined. Gradually whisk in lemon juice, egg yolks, and water, stirring until completely smooth with no lumps.
04 - Place the saucepan over medium heat and whisk constantly for 6 to 8 minutes until the mixture thickens significantly and comes to a gentle boil. Remove from heat and whisk in the butter until fully melted and incorporated.
05 - Pour the hot lemon filling directly into the prepared graham cracker crust, spreading it into an even layer.
06 - In a clean, grease-free mixing bowl, beat egg whites and cream of tartar with an electric mixer on medium speed until soft peaks form. Gradually add sugar, about one tablespoon at a time, beating continuously until stiff, glossy peaks hold their shape.
07 - Spread the meringue evenly over the hot filling, making sure to seal the edges against the crust to prevent shrinking. Bake for 12 to 15 minutes until the meringue peaks are golden brown.
08 - Allow the pie to cool completely at room temperature, then refrigerate for at least 2 hours before slicing to ensure the filling sets properly.