Prepare the Dough: In a food processor, combine the flour, sugar, and salt. Add the cold cubed butter and pulse until the mixture resembles coarse crumbs.
Add Ice Water: Gradually add ice water, one tablespoon at a time, and pulse until the dough comes together.
Form the Crust: Turn the dough out onto a lightly floured surface and shape it into a disk. Wrap in plastic wrap and refrigerate for at least 1 hour.
Roll Out the Dough: On a floured surface, roll out the chilled dough into a circle large enough to fit into a 9-inch pie dish. Transfer the dough to the pie dish and trim any excess. Crimp the edges decoratively and refrigerate while you prepare the filling.
For the Lemon Filling:
Preheat the Oven: Preheat the oven to 350°F (175°C).
Prepare the Filling: In a saucepan, whisk together the sugar and cornstarch. Gradually whisk in the water until smooth. Cook over medium heat, stirring constantly, until the mixture thickens and comes to a boil.
Temper the Eggs: In a separate bowl, whisk the egg yolks. Gradually whisk in about half of the hot sugar mixture to temper the eggs, then return the egg mixture to the saucepan.
Cook the Filling: Cook the mixture over medium heat, stirring constantly, until thickened, about 2 minutes. Remove from heat and stir in the lemon zest, lemon juice, and butter until smooth.
Fill the Crust: Pour the lemon filling into the prepared pie crust and smooth the top.
For the Meringue Topping:
Make the Meringue: In a clean, dry bowl, beat the egg whites with an electric mixer on medium speed until foamy. Add the cream of tartar and continue to beat until soft peaks form. Gradually add the sugar, one tablespoon at a time, and beat on high speed until stiff, glossy peaks form.
Top the Pie: Spoon the meringue over the hot lemon filling, spreading it to the edges to seal in the filling.
Bake the Pie: Bake the pie in the preheated oven for 10-12 minutes, or until the meringue is golden brown.
Cool and Serve: Allow the pie to cool completely on a wire rack before slicing and serving.