In a medium saucepan, combine sugar, flour and salt. Stir in milk; cook and stir over medium-high heat until thickened and bubbly. Reduce heat; cook and stir 2 minutes longer.
Remove from the heat; gradually stir about 1 cup of hot mixture into beaten eggs. Return all to saucepan; cook and stir over medium heat until nearly boiling. Reduce heat; cook and stir about 2 minutes more (do not boil).
Remove from the heat; stir in 1 cup coconut, butter and vanilla. Pour into pie shell; sprinkle with remaining coconut. Chill for several hours before serving. Refrigerate leftovers. Yield: 6-8 servings.