In large saucepan, stir together 1-1/2 cups of the sugar, 1/3 cup of the cornstarch, and the salt. Gradually stir in the 1-1/2 cups cold water and the lemon juice until smooth. In small bowl, beat egg yolks until well blended. Stir into sugar mixture until blended. Add butter. Cook over medium heat, stirring constantly, until mixture thickens and boils. Boil, stirring constantly, 1 minute. Remove from heat. Stir in lemon peel. Pour hot filling into pie shell. In large mixing bowl at high speed, beat egg whites with cream of tartar until foamy. Add the remaining 1/2 cup sugar, 1 Tbsp. at a time, beating constantly until sugar is dissolved and whites are glossy and stand in soft peaks. (Rub just a bit of meringue between thumb and forefinger to feel if sugar has dissolved.) Into small saucepan, sprinkle the remaining 1 Tbsp. cornstarch. Add the remaining 1/3 cup cool water. Let stand 1 minute. Stir well. Bring to boiling, stirring constantly. Let cool a few minutes. Add to egg whites, 1 to 2 Tbsp. at a time, beating constantly. Beat in vanilla. Spread meringue over hot filling, starting with small amounts at edges and sealing to crust all around. Cover pie with remaining meringue, spreading evenly in attractive swirls. Bake in preheated 325-degree oven until peaks are lightly browned, about 16 to 18 minutes. Cool on wire rack, about 30 minutes to 1 hour. Serve immediately or refrigerate, uncovered, until serving. Garnish with lemon peel twists and mint leaves, if desired. Refrigerate any leftovers. Makes 6 to 8 servings. (Note: When pie is refrigerated, beads may form on meringue. Gently touch beads with tip of folded paper towel until absorbed.)