Preheat & Prep
Preheat your oven to 350°F. If you haven’t already, make sure your baked crust is cooled and ready to go.
Make the Lemon Filling
In a medium saucepan, whisk together sugar and cornstarch.
Slowly add the water, whisking until smooth.
Cook over medium heat, stirring constantly, until the mixture thickens and begins to bubble.
Remove from heat and temper your egg yolks: add a spoonful of the hot mixture into the yolks, whisking quickly.
Pour the yolk mixture back into the saucepan.
Return to heat and cook until thick and glossy.
Stir in butter, lemon juice, and lemon zest.
Pour into the Crust
Spread the hot lemon filling into your prepared crust. Working with a warm filling helps the meringue adhere better (goodbye, gaps!).
Make the Meringue
Place your large egg whites into a clean bowl (any grease will deflate them).
Using a stand mixer with the whisk attachment, beat on medium speed until frothy.
Add cream of tartar.
Increase the speed to high and slowly add the sugar, one tablespoon at a time.
Continue to beat egg whites until soft peaks form — then keep going until you reach glossy, stiff peaks.
Top the Pie
Spread the meringue over the warm filling, making sure it touches the crust edges (this helps prevent shrinking). Use the back of a spoon to create swoops and curls — this is my favorite part. It’s like pie-shaped sculpture.
Bake
Bake in the preheated oven for 15–18 minutes, or until the meringue is golden brown.
Let the pie cool completely before slicing (trust me, it’s worth the wait). The smell alone will tease you long before the timer beeps.