In heavy saucepan combine 1-1/2 cups sugar, cornstarch, flour and salt. Gradually stir in water until well blended. Bring to a boil, stirring, over medium heat. Boil 3 minutes. Remove from heat. Whisk about half the mixture into egg yolks. Whisk egg yolk mixture back into hot mixture. Re to a boil, stirring constantly. Boil, stirring, 3 minutes more. Add lemon peel, juice and butter; cook, stirring, about 2 minutes more, until very thick. Cover and set aside while making the meringue. Preheat oven to 350°F. In mixer bowl beat egg whites and cream of tartar until foamy. Gradually beat in remaining 1/2 cup sugar until soft peaks form. Beat in vanilla. Spoon hot filling into baked pie shell. Starting at edge of pie, spread meringue over filling. Bake 15 to 20 minutes, until meringue is golden brown. Cool 4 hours at room temperature before serving. Makes 8 servings, 415 calories each. dess 81