On lightly floured pastry cloth, roll the pastry to an 11 inch circle, rolling with light strokes from center to edge. Fold pastry in half; with fold in center, carefully transfer to a 9 inch pie plate. Unfold; fit into a pie plate, pressing gently toward the center. Fold edge of crust under; press into an upright rim. Crimp edge decoratively, using thumb and forefinger. Refrigerate 1/2 hour. Preheat oven to 450 degrees. Prick entire surface evenly with fork. Bake 8 to 10 minutes, or until golden-brown. Cool on rack. In medium sauce pan, combine cornstarch, flour, 1 3/4 cups sugar and salt, mixing well. Gradually add 2 cups water, stirring until smooth. Overy medium heat, bring to boiling, stirring occasionally; boil 1 minute, until shiny and translucent. Quickly stir some of hot mixture into yolks. Pour back into hot mixture; stir to blend. Return to heat; cook over low heat 5 minutes, stirring occasionally. Remove from heat; stir in lemon juice, lemon peel and butter. Pour into pie shell. Preheat oven to 400 degrees. In medium bowl, with mixer at medium speed, beat whites with cream of tartar until frothy. Gradually beat in sugar, 2 T at a time, beating after each addition. Beat at high speed until stiff peaks form when beater is slowly raised. Spread meringue over lemon filling, carefully sealing to edge of the crust and swirling thetop decoratively. Bake 7 to 9 minutes, or until the meringue is golden-brown. Let cool completely on rack 2 1/2 to 3 hours. Cut with wet knife.