Meanwhile, in 1-quart heavy saucepan, mix sugar and cornstarch. Gradually stir in orange juice, 1/4 cup water and the egg yolks. Cook over medium heat, stirring constantly, until thickened. Cook and stir 1 minute longer. Remove from heat; stir in 2 tablespoons butter and the orange peel. Transfer filling to small bowl. Cover; refrigerate 30 minutes.