01 -
In a medium saucepan, whisk together sugar, flour, cornstarch, and salt.
02 -
Stir in water, lemon juice, and lemon zest. Cook over medium-high heat, stirring frequently, until mixture comes to a boil.
03 -
Stir in butter.
04 -
Gradually whisk about 1/2 cup of the hot mixture into the beaten egg yolks to temper them, then slowly whisk the egg yolk mixture back into the saucepan.
05 -
Bring to a gentle boil and cook for 2 more minutes, stirring constantly, until thickened.
06 -
Remove from heat and pour the filling into the pre-baked pie crust.
07 -
Preheat oven to 350°F (175°C).
08 -
In a clean, dry bowl, beat egg whites and cream of tartar on medium speed until soft peaks form.
09 -
Gradually add sugar, 1 tablespoon at a time, beating until stiff, glossy peaks form. Beat in vanilla extract.
10 -
Spread the meringue over the hot lemon filling, sealing the edges at the crust to prevent shrinking.
11 -
Bake for 15-20 minutes, or until the meringue is golden brown.
12 -
Cool completely at room temperature, then chill in the refrigerator for at least 2 hours before serving.