CRUST:
2 1/4 cups all-purpose flour
(or preferably King Arthur Mellow Pastry Blend)*
1 teaspoon salt
1 teaspoon sugar
1 1/2 sticks very cold unsalted butter -- cut in 1" cubes
1 teaspoon white vinegar
1/3 cup ice water
FILLING:
1 cup sugar
1/4 cup cornstarch
3 tablespoons all-purpose flour
1/4 teaspoon kosher salt
1 1/2 cups water
1 tablespoon lemon zest
1/3 scant cup fresh lemon juice (about 2 lemons)
1/4 teaspoon lemon extract (preferably Lemon Oil)*
3 egg yolks
2 tablespoons soft butter
MERINGUE:
4 egg whites
1/4 teaspoon cream of tartar
Pinch kosher salt
1/2 cup sugar
CRUST (stand mixer): Fit mixer with paddle attachemnt. In the bowl, mix flour, salt and sugar 1 minute. Add butter and mix just until mixture is crumbly (should still be able to see pieces of butter). In a measuring cup mix water and vinegar together; ad a couple of ice cubes to keep it cold. With the mixer running at medium speed, drizzle in the water-vinegar mixture and mix just until a dough forms (you should still see pieces of butter). Turn dough out onto a floured surface; use hands to bring it together into a ball and then into a round flat disk (do not overwork it). Wrap dough in plastic wrap and refrigerate at least 30 minutes before using (or up to 48 hours, or freeae up to 1 month). If frozen, let thaw overnight in refrigerator and let come to room temperature before using.
Dust work surface and top of dough with flour. Roll from center out in all directions into a circle 2 inches larger than pie plate. Carefully roll crust around rolling pin; gently unroll it over the pie plate (don't worry if edges tear slightly---patch it). Use scissors to trim excess dough to within 3/4-inch of the rim. Turn crust underitself to make a thick edge, pressing it firmly against the pan. Crimp the edges. Chill 20-30 minutes before baking pie.
Preheat oven to 375 degrees; Prick the bottom and sides of the pastry with a fork. Line the pastry with parchment paper or waxed paper and fill with pie weights or dried beans. Bake until lightly browned, 20 to 25 minutes. Remove from oven and remove the weights and paper. Transfer the pie shell to a rack and cool completely.
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FILLING: In a medium heavy saucepan, combine sugar, cornstarch, flour and salt; gradually add water, stirring. In a medium bowl, combine egg yolks, lemon zest, lemon juice, and lemon extract; set aside. Bring the sugar-water mixture to a boil, stirring constantly. Cook and stir constantly over medium heat until thickened and bubbly, about 2 minutes. Reduce heat to low; cook and stir constantly 2 minutes. Remove from heat. Using a medium whisk, whisk a few tablespoonfuls of the hot filling mixture slowly into egg yolk mixture (bottom of bowl should feel warm to the touch). Transfer egg mixture to remaining filling in the saucepan over low heat; stir in the butter and cook 3 minutes, stirring constantly. Pour hot filling into pastry shell.
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MERINGUE: Preheat oven to 400 degrees. In a mixing bowl with mixer at high speed, beat egg whites, cream of tartar and salt until frothy. Gradually sprinkle in sugar 2 tablespoons at a time, beating until sugar completely dissolves and egg whites stand in stiff glossy pweaks when beaters are lifted. Immediately spread over warm filling, sealing edges to pastry and making a swirl on top. Bake 7-8 minutes or until the meringue is golden. Cool pie on a wire rack away from drafts. Refrigerate at least 1 hour before serving.
* Mellow Pastry Blend Flour and Lemon Oil may be purchased on-line from King Arthur Flour Company and really improves the flavors and consistency.