1. Blend cornstarch, 1 1/2 cups sugar & salt in a sauce pan, stir in water - gradually. Cook over med. heat stirring constantly, until mixture comes to a boil. Boil 1 minute. Stir 1/2 of mixture into egg yolks, and then stir into mixture in saucepan. Cook over low heat stirring constantly, 2 min. and remove from heat. Add butter, lemon rind & juice.
2. Pour into baked pie shell. Beat egg whites & cream of tartar until foamy, beat in 1/2 cup sugar - gradually, continue beating until meringue forms stiff, glossy peaks. Spread into pie filling, being sure the meringue touches crust all around.
3. Bake at 350°F for 15 to 20 min. or until meringue is tipped with brown. Cool at room temperature before serving.