Prepare Baked Pastry Shell; set aside. Separate egg yolks from whites. Set aside yolks for filling and whites for Five-Egg White Meringue.
Preheat oven to 325 degrees F. For filling, in a medium saucepan stir together sugar and cornstarch. Stir in lemon peel (if desired), the water, and lemon juice. Cook and stir over medium heat until thickened and bubbly. Remove from heat.
Lightly beat egg yolks with a fork. Gradually stir half of the hot lemon mixture into the yolks. Return egg yolk mixture to saucepan. Bring to a gentle boil; reduce heat. Cook and stir for 2 minutes more. Remove from heat. Stir in butter pieces until melted. Cover filling and keep warm.
Prepare Five-Egg White Meringue. Pour warm filling into Baked Pastry Shell. Immediately spread meringue over filling; seal to edge of pastry. Using the back of a spoon, add high peaks to the meringue. Bake for 30 minutes. Cool on a wire rack for 1 hour. Chill for 5 to 6 hours before serving; cover for longer storage.
Baked Pastry Shell
Preheat oven to 450 degrees F. In a medium bowl stir together flour and salt. Using a pastry blender, cut in shortening and butter until pieces are pea size. Sprinkle 1 tablespoon ice water over part of the flour mixture; toss gently with a fork. Push moistened dough to side of bowl. Repeat with additional ice water, 1 tablespoon at a time (1/4 to 1/3 cup total), until all of the flour mixture is moistened. Gather mixture into a ball, kneading gently until it holds together. On a lightly floured surface use your hands to slightly flatten pastry. Roll pastry from center to edge into a 12-inch circle. Wrap pastry circle around rolling pin; unroll into a 9-inch pie plate. Ease pastry into pie plate without stretching it. Trim pastry to 1/2 inch beyond edge of pie plate. Fold under extra pastry even with edge of pie plate. Crimp edge as desired. With a fork, prick side and bottom of pastry. Line pastry with a double thickness of foil. Bake for 8 minutes. Remove foil. Bake for 6 to 8 minutes more or until pastry is golden. Cool on a wire rack.
Five-Egg White Meringue
Allow egg whites to stand at room temperature for 30 minutes. In a mixing bowl combine whites, vanilla, and cream of tartar. Beat with an electric mixer on medium speed about 1 minute or until soft peaks form (tips curl). Gradually add sugar, 1 tablespoon at a time, beating on high speed about 6 minutes or until mixture forms stiff, glossy peaks (tips stand straight) and sugar dissolves (rub a small amount between two fingers; it should feel completely smooth). Immediately spread meringue over hot pie filling, sealing to edge of pastry. Bake as directed in recipe.