Prepare pie crust: Roll out pie dough and place in a 9-inch pie dish. Crimp edges decoratively. Preheat oven to 375°F (190°C).

Blind bake crust: Line crust with parchment paper and fill with pie weights. Bake for 15 minutes, remove weights and parchment, then bake 8-10 minutes more until lightly golden. Reduce oven to 350°F (177°C).

Prepare filling: Whisk egg yolks in a medium bowl and set aside. In a saucepan, whisk together water, 1 cup sugar, cornstarch, 1/4 teaspoon salt, lemon juice, and lemon zest. Cook over medium heat for 6 minutes, whisking frequently until thickened and bubbling.

Temper egg yolks: Very slowly stream a few spoonfuls of hot lemon mixture into the egg yolks while whisking constantly. Then slowly whisk the tempered egg mixture back into the saucepan. Cook over medium heat until thick and bubbling, about 2 minutes.

Finish filling: Remove from heat and whisk in butter until smooth. Pour hot filling into the warm pie crust. Set aside while preparing meringue (keep filling warm).

Make meringue: Beat egg whites and cream of tartar on medium speed for 1 minute. Increase to high speed and beat until soft peaks form, about 4 minutes. Gradually add 1/2 cup sugar and 1/8 teaspoon salt, beating on high until stiff, glossy peaks form, about 2 minutes.

Assemble pie: Spread meringue over warm filling, making sure it touches all edges of the crust to seal. Create decorative peaks with the back of a spoon.

Bake pie: Bake for 20-25 minutes until meringue is golden brown. If browning too quickly, tent with foil. Cool at room temperature for 1 hour, then refrigerate for 4 hours before slicing.