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 for 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 for about 2 minutes more (do not boil).
Remove from the heat; stir in 1 cup coconut, butter and vanilla extract.
Pour into pie shell; sprinkle with remaining coconut.
Chill for several hours before serving.
Refrigerate leftovers.
Notes
Photo credit: a5/dd5da665 Stacy Spensley on Visualhunt / CC BY