Step 1: Preheat Oven

Preheat your oven to 325°F (165°C). Make sure the pie crust is baked and ready.

Step 2: Make the Lemon Filling

In a medium saucepan, whisk together the sugar, flour, cornstarch, and salt.
Stir in water, lemon juice, and lemon zest.
Cook over medium-high heat, stirring frequently, until the mixture comes to a boil.
Stir in the butter.

Step 3: Temper the Egg Yolks

Place egg yolks in a small bowl. Gradually whisk in about 1/2 cup of the hot lemon mixture to temper.
Slowly pour the tempered egg yolk mixture back into the saucepan, whisking constantly.

Step 4: Thicken and Fill

Bring the mixture back to a gentle boil, stirring constantly until thickened.
Remove from heat and pour the filling into the pre-baked pie crust.

Step 5: Make the Meringue

In a clean glass, metal, or ceramic bowl, beat the egg whites with an electric mixer until foamy.
Gradually add sugar and continue beating until stiff peaks form.

Step 6: Assemble the Pie

Quickly spread the meringue over the hot lemon filling.
Make sure to seal the meringue to the crust edges to prevent shrinking.
Use a spoon to create decorative peaks on the surface if desired.

Step 7: Bake

Bake the pie for 20 to 25 minutes, or until the meringue is golden brown.

Step 8: Cool and Serve

Let the pie cool completely before slicing. Serve and enjoy the sweet-tart perfection!