In a pot combine sugar, cornstarch and salt. Gradually stir in milk. Cook slowly, stirring constantly, until mixture thickens and boils. Boil 1 minute. Remove from heat.
Place egg yolks in a bowl. Stir in 1/2 sugar mixture. Stir egg mixture in pot. Boil, stirring constantly, for 1 minute longer. Remove from heat. Stir in vanilla and butter. Add 3/4 cup coconut. Pour immediately into pie shell. Chill thoroughly. Top with whipped cream. Sprinkle remaining coconut on top. Yields one 9 inch pie.