Preheat oven to 375 degrees. Make the crust: Whisk together flour, sugar, 1/2 teaspoon salt, and the lemon zest in a large bowl. Cut in butter with a pastry cutter or your fingers until dough begins to hold together.
Stir together 1 tablespoon water and vanilla, then mix into dough. Shape dough into a disk, and wrap in plastic wrap. Refrigerate for 30 minutes.
Using your fingers, press dough evenly into bottom and up sides of a 9-inch fluted tart pan with a removable bottom. Freeze for 30 minutes.
Bake tart shell until golden, about 25 minutes. Let cool completely.
Meanwhile, make the lemon curd: Whisk together eggs, egg yolks, sugar, and cornstarch in a medium saucepan. Whisk in lemon zest and juice. Cook over medium-low heat, stirring constantly, until thick enough to coat the back of a wooden spoon, about 7 minutes. Remove from heat and whisk in butter, 1 piece at a time.
Pour filling into cooled tart shell. Bake until filling is browned, slightly puffed, and set, about 30 minutes. Let cool completely.
The tart can be refrigerated up to 3 days.
Excellent - curd took 2 mins vs. 8 mins so watch carefully.
And dough is just enough for 9" pan - don't try to use a larger pan! I very thinly sliced another lemon and put the rounds on top. looked beautiful.