Bake pie shell then reduce oven temperature to 350 degrees.
In medium saucepan, combine sugar, cornstarch, flour and salt; mix well. Gradually stir in cold water & grapefruit juice until smooth. Cook over medium heat stirring constantly, until mixture boils; boil 1 minute. Remove from heat, stir about 1/4 cup into egg yolks. Return yolk mixture to saucepan & cook over low heat until mixture boils stirring constantly; boil 1 minute. Remove from heat, add butter & grapefruit peel.
Pour into cooled baked crust, top with your favorite meringue recipe and bake as directed.

Make this in November or early December while grapefruit are still tart enough to make a good pie. You can use this recipe to make a meringue style key lime pie. Use 1/2 cup of bottled Key Lime juice and increase water to 1 1/4 cups.