In a saucepan, combine sugar, cornstarch, flour and salt; gradually add milk until smooth. Bring to a boil over medium heat. Cook and stir for 2 minutes or until thickened. Remove from the heat. Gradually stir a small amount into egg yolks; return all to the pan, stirring constantly. Bring to a gentle boil; cook and stir for 2 minutes. Remove from the heat; stir in butter and vanilla. Cool to lukewarm; fold in 2/3 cup coconut. Pour into pastry shell. Refrigerate until set, about 3 hours. Meanwhile, toast the remaining coconut. To serve, top with whipped cream and sprinkle with toasted coconut. Store in the refrigerator.