Roll out your chilled pie dough on a board. Place it gently into your clean pie plate. Trim the edges and crimp them with your fingers.
Line the dough with parchment paper and weights. Bake the crust until it looks golden brown. Let it cool completely on a wire rack.
Whisk sugar, cornstarch, and salt in a pan. Add water, lemon juice, and lemon zest slowly. Cook over medium heat until the mix thickens.
Beat your egg yolks in a small bowl. Add a little hot lemon mix to them. This tempers the eggs so they do not scramble.
Pour the yolk mixture back into the saucepan. Cook for two more minutes while whisking constantly. Remove from heat and stir in the butter.
Pour the warm lemon curd into your crust. Smooth the top with a clean rubber spatula. Set this aside while you make the topping.
Beat egg whites and cream of tartar together. Add sugar slowly while the mixer is running. Whip until the peaks stand up very straight.
Pile the meringue on top of the filling. Spread it all the way to the crust. This prevents the meringue from shrinking during baking.
Bake the pie until the meringue turns brown. This usually takes about ten to fifteen minutes. Watch it closely so it does not burn.