01 - Preheat oven to 350°F. Combine graham cracker crumbs, sugar, and melted butter in a mixing bowl until evenly moistened. Press the mixture firmly into the bottom and up the sides of a 9-inch pie pan.
02 - Bake the crust for 8 minutes until set and lightly toasted. Remove from the oven and set aside to cool.
03 - In a medium saucepan, whisk together sugar, cornstarch, salt, and lemon zest. Gradually whisk in the lemon juice, egg yolks, and water until completely smooth.
04 - Place the saucepan over medium heat and whisk constantly for 6 to 8 minutes until the mixture thickens and reaches 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 evenly.
06 - In a clean, grease-free bowl, beat egg whites and cream of tartar with an electric mixer until soft peaks form. Gradually add sugar, one tablespoon at a time, beating continuously until stiff, glossy peaks hold their shape.
07 - Spread the meringue over the hot filling, making sure to seal the edges against the crust to prevent shrinking or weeping.
08 - Bake for 12 to 15 minutes until the meringue peaks are golden brown. Watch carefully to avoid over-browning.
09 - Cool the pie at room temperature for 1 hour, then refrigerate for at least 2 hours before slicing and serving.