01 - Set oven temperature to 350°F and prepare for baking.
02 - Combine graham cracker crumbs and sugar in a bowl. Add melted butter and stir until evenly moistened. Press mixture firmly into the bottom and sides of a 9-inch pie dish. Bake for 8 to 10 minutes until lightly golden, then cool slightly.
03 - In a medium saucepan, whisk sugar, cornstarch, and salt. Gradually add water, whisking to combine. Cook over medium heat, whisking constantly until mixture thickens and boils, about 5 minutes.
04 - In a separate bowl, beat egg yolks. Gradually whisk in half a cup of the hot lemon mixture to temper yolks, then return all to the saucepan. Boil for one minute while whisking continuously, then remove from heat.
05 - Stir in fresh lemon juice, lemon zest, and butter. Mix until smooth and glossy, then pour filling into the crust, smoothing the surface.
06 - Beat egg whites and cream of tartar on medium-high speed until soft peaks form. Gradually add sugar and continue beating until stiff, glossy peaks form. Fold in vanilla extract.
07 - Spread meringue evenly over hot lemon filling, sealing edges to crust to prevent shrinkage. Create decorative swirls with the back of a spoon.
08 - Bake assembled pie at 350°F for 15 to 18 minutes until meringue turns golden brown.
09 - Allow pie to cool to room temperature. Refrigerate for at least 2 hours to ensure firm slices before serving.