01 - Set oven temperature to 350°F (175°C).
02 - Combine graham cracker crumbs and sugar in a medium bowl. Stir in melted butter until mixture is evenly moistened. Press firmly onto bottom and sides of a 9-inch pie dish. Bake for 8 to 10 minutes until lightly golden. Allow to cool slightly.
03 - In a medium saucepan, whisk together sugar, cornstarch, and salt. Gradually add water, whisking until smooth. Cook over medium heat, whisking constantly, until mixture thickens and reaches a boil, about 5 minutes.
04 - In a separate bowl, whisk egg yolks. Slowly whisk in half a cup of the hot mixture to temper yolks. Return yolk mixture to saucepan, whisk constantly, and boil for 1 minute. Remove from heat.
05 - Stir in lemon juice, lemon zest, and butter until the filling is smooth and glossy. Pour filling into crust and smooth the surface evenly.
06 - Using a clean bowl, beat egg whites and cream of tartar on medium-high speed until soft peaks form. Gradually add sugar, continuing to beat until stiff and glossy peaks develop. Fold in vanilla extract.
07 - Spread meringue evenly over the hot lemon filling, sealing edges to the crust to prevent shrinking. Use the back of a spoon to create decorative swirls.
08 - Bake at 350°F (175°C) for 15 to 18 minutes until meringue is golden brown.
09 - Allow pie to cool to room temperature, then refrigerate for a minimum of 2 hours before serving to ensure clean slices.