How to Make It
Make the crust: Preheat oven to 400°F. Place almonds in a food processor; pulse until finely chopped, about 6 times. Add flour, powdered sugar, and salt; pulse twice to combine. Add butter; pulse until small, moist clumps form, about 13 to 16 times (dough will be crumbly but it will hold together when pressed between fingers; you don’t want the dough to form a ball, but you also don’t want lots of dry flour).
Transfer dough to a 9-inch pie pan lightly coated with cooking spray. Pat dough into bottom and up sides of pie pan; pierce bottom of dough with a fork. Place in freezer for 10 minutes. Remove dough from freezer; line with parchment paper and pie weights or dried beans. Bake at 400°F until lightly browned, 15 to 18 minutes. Carefully remove parchment paper and pie weights. Bake until evenly browned, about 5 minutes. Place on a wire rack to let cool.
Make the filling: Whisk together granulated sugar, cornstarch, and salt in a large, heavy
saucepan. Whisk in 1 1/3 cups water and lemon juice. Cook over medium, stirring almost constantly, until bubbly and thick, about 6 minutes. Place egg yolks in a medium bowl.
Add about one-fourth of hot lemon juice mixture to egg yolks, whisking constantly.
Gradually add remaining hot lemon juice mixture, whisking constantly. Pour mixture back into
pan; cook over medium, whisking constantly, until bubbly, about 2 minutes. Remove
from heat. Stir in lemon zest. Add butter; stir until butter melts. Place saucepan into an
ice bath in a large bowl. Let cool to room temperature (or cooler), whisking occasionally, about 8 minutes. Spoon mixture into cooled crust. Loosely cover with plastic wrap, and refrigerate until set, about 1 hour.
Make the meringue: Place egg whites in the bowl of a stand mixer. Add cream of tartar, vanilla, and salt. Beat on medium speed just until soft peaks form.
Combine granulated sugar and 1/4 cup water in a small, heavy saucepan; stir just to moisten sugar. Bring to a boil; cook, without stirring, until a candy thermometer registers 250°F, about 6 minutes. With stand mixer running on medium-low speed, slowly pour hot sugar syrup down side of bowl into egg white mixture. Increase speed to medium, and gradually increase up to high. Beat until stiff peaks form. Spoon meringue over pie. Lightly brown meringue under a broiler or with a kitchen torch, if desired.