01 - Set the oven temperature to 375°F (190°C).
02 - Combine flour and salt in a bowl. Cut in cold butter until mixture resembles coarse crumbs. Gradually add ice water, stirring until the dough forms. Shape into a disk, wrap in plastic, and chill for 30 minutes.
03 - Roll out dough on floured surface, fit into a 9-inch pie dish, trim and crimp edges. Prick base with fork. Line with parchment and fill with pie weights or dried beans. Bake 15 minutes, remove weights and parchment, bake 10 minutes more until golden. Cool completely.
04 - In a saucepan, whisk sugar, cornstarch, and salt. Gradually add water, lemon juice, and zest. Cook over medium heat, stirring until thick and bubbly.
05 - Beat egg yolks separately. Slowly whisk some hot lemon mixture into yolks to temper, then return yolk mixture to saucepan. Cook 2 minutes, stirring constantly. Remove from heat; stir in butter. Pour filling into baked crust.
06 - Beat egg whites and cream of tartar until soft peaks form. Gradually add sugar, beating to stiff glossy peaks. Fold in vanilla extract.
07 - Spread meringue evenly over hot lemon filling, sealing edges to crust. Shape decoratively with swirls.
08 - Bake at 375°F (190°C) for 10 to 12 minutes until meringue is golden brown.
09 - Allow to cool at room temperature, then refrigerate for at least 2 hours before serving.