01 - Set oven temperature to 375°F.
02 - Combine flour, salt, and sugar in a bowl, then rub in cold cubed butter until mixture resembles coarse crumbs. Mix in egg yolk and ice water just until dough forms. Shape into a disk, wrap, and refrigerate for 30 minutes.
03 - Roll out dough and line a 9-inch pie dish. Trim edges, prick base, cover with parchment paper, and fill with baking beans. Bake for 15 minutes. Remove beans and parchment, bake an additional 10 minutes until lightly golden. Let cool.
04 - In a saucepan, whisk sugar, cornstarch, and salt. Gradually add water, cooking over medium heat while stirring until thick and bubbling. Continue cooking for 1 minute.
05 - Whisk egg yolks separately. Slowly add a few spoonfuls of hot filling mixture to yolks, then return all to saucepan. Stir constantly and cook for 2 minutes. Remove from heat and mix in lemon juice, zest, and butter until smooth. Pour filling into cooled crust.
06 - Beat egg whites with cream of tartar until soft peaks form. Gradually add sugar, continuing to beat until glossy stiff peaks develop. Fold in vanilla extract.
07 - Spread meringue evenly over hot lemon filling, sealing edges to crust. Create decorative peaks by swirling with a spoon. Bake for 10 to 12 minutes until meringue turns golden.
08 - Allow dessert to cool to room temperature, then refrigerate for at least 2 hours before serving.