In a saucepan mix sugar, cornstarch, flour, and salt. Gradually add hot water, stirring constantly. Cook and stir over high heat until mixture comes to a boil. Reduce heat, cook stirring for 2 minutes. Stir a small amount of hot mixture into egg yolks then add to pan. Bring to a boiling and cook 2 minutes stirring constantly. Add butter and lemon peel. Slowly add lemon juice, mixing well. Pour into pie crust and top with meringue. Bake 350? for 12-15 minutes.