Ground Graham crackers in a food processor, mix in melted butter until the crumbs hold in a clump when pressed together.
Press the crust into the bottom and up the side of a pie pan using the flat bottom of a small glass or measuring cup. Place in the refrigerator to set for about 15 minutes while the oven is preheating.
Preheat the oven to 375°F and bake the crust for 10 minutes.
Turn off the oven and remove the pie crust. Set it on a wire rack to cool.
Make the lemon filling:
Whisk together the sugar and lemon zest. Add the salt and cornstarch, whisk to distribute evenly. Set aside.
Melt butter in a saucepan over medium heat. Add water, lemon juice, and the sugar/cornstarch mixture, stir to make sure the cornstarch dissolves. Add the egg yolks and cook the mixture, whisking constantly, until it thickens and some bubbles burst at the surface, about 5 mins.
Strain the filling through a fine mesh sieve into a clean bowl. Set aside to cool.
Transfer cool lemon filling into the cool pie crust, cover with plastic wrap and refrigerate until the filling sets completely, about 4 hours.
Make the meringue:
Whisk together egg whites and sugar in a heatproof bowl over a pot of simmering water. Continue whisking until the egg white mixture reaches 160°F.
Transfer egg white mixture into a stand mixer bowl and add cream of tartar. Beat with the wire whisk attachment on medium speed until it is fluffy and reaches soft peaks.
Sprinkle in the salt and stream in the vanilla extract. Then continue beating until the meringue is shiny and stiff peaks form.
Assemble the pie:
Add the meringue on top of the lemon filling. Use a spatula to push the meringue out to the edges leaving a dome in the middle. Use the back of a spoon to make little peaks all around.