Combine the sugar, cornstarch, and milk, mix well. Add the beaten egg yolks. Cook over medium heat, stirring constantly, until the mixture begins to boil and is thickened. Remove from heat. Add butter, vanilla, crushed pineapple, coconut, thoroughly combining all. Pour the mixture into pie shell and chill. When chilled, cover top with whipped cream. Sprinkle with roasted coconut.