On a lightly floured surface, roll dough to a 1/8-in.-thick circle; transfer to a 9-in. pie plate. Trim to 1/2 in. beyond rim of plate; flute edge. Refrigerate 30 minutes. Preheat oven to 425°. , Line crust with a double thickness of foil. Fill with pie weights, dried beans or uncooked rice. Bake on a lower oven rack until edge is golden brown, 20-25 minutes. Remove foil and weights; bake until bottom is golden brown, 3-6 minutes longer. Cool on a wire rack. Reduce oven setting to 350°., In a medium saucepan, combine sugar, cornstarch, flour and salt. Gradually stir in water. Cook and stir over medium heat until thickened and bubbly. Reduce heat; cook and stir 2 minutes more. Remove from the heat. , Gradually stir 1 cup hot mixture into egg yolks; return all to saucepan. Bring to a boil. Cook and stir for 2 minutes. Remove from the heat. Stir in the butter, lemon juice and zest until smooth. Pour into pie crust. , In a bowl, beat egg whites and salt until stiff (but not dry) peaks form. Gradually beat in sugar until soft peaks form. Spread over pie, sealing edge to crust. Bake at 350° until meringue is golden, 12-15 minutes. Cool. Store any leftovers in the refrigerator.