To Make the Pie Crust: Mix together the flour, sugar and salt in food processor. Add butter and shortening. Using on/off pulses, process until mixture resembles coarse meal.
Sprinkle the ice water over mixture. Process just until moist clumps form, adding more ice water by teaspoonfuls if dough is dry. Gather dough into a ball; flatten into a disk. Wrap in plastic; chill until dough is firm enough to roll out, about 30 minutes.
Roll out dough between two pieces of plastic wrap to a 12-inch round. Transfer dough to a 9" pie dish. Fold overhang under. Crimp edges and refrigerate.
Preheat oven to 450 degrees F. Prick entire surface of pie crust evenly with a fork. Bake 8 to 10 minutes or until golden brown. Cool on rack.
Make the Lemon Filling: In medium saucepan, combine cornstarch, flour, 1 3/4 cups sugar and salt, mixing well. Gradually add 2 cups water, stirring until smooth. Over medium heat, bring to boil, stirring occasionally; boil 1 minute, till 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. (Note: Avoid tasting due to enzymes in saliva breaking down the starch and making it runny.) Remove from heat; stir in lemon juice, lemon peel and butter. Pour into pie shell. Preheat oven to 400 degrees F.
To Make the Meringue: In medium bowl, with mixer at medium speed, beat whites with cream of tartar until frothy. Gradually beat in sugar, 2 tablespoons 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 crust and swirling the top decoratively. Bake 7 to 9 minutes, or until the meringue is golden brown. Let cool completely on rack 2 1/2 to 3 hours.