In a 2- to 3-qt. saucepan, combine sugar, cornstarch and salt. Using a wire whisk, gradually blend in orange juice until smooth. Add egg yolks and blend thoroughly. Add lemon juice and butter. Cook on medium heat, stirring constantly, and gradually bring to a boil. Reduce heat as mixture begins to thicken. Boil slowly for 1 minute. Remove from heat; stir in peel. Pour hot filling into pie shell. Let stand, allowing a thin film to form on top.
Meanwhile, for meringue, beat egg whites in a small bowl until foamy. Add cream of tartar; beat on high until soft peaks form. Reduce speed to medium; add sugar gradually, about 1 tablespoon at a time. beat on high until stiff and glossy.
Spoon meringue around edge of filling. Using a spatula, push meringue gently against inner edge of crust, sealing well. Swirl meringue into center of pie.
Bake at 350° for 12-15 minutes or until meringue is golden brown. Cool on wire rack at room temperature for 2 hours before serving. To cut, use a sharp knife dipped in hot water.