Beat the egg yolks with the remaining 1/2 cup milk.
Mix the sugar, salt and cornstarch. Add this mixture to the egg and milk mixture.
Take 1/4 cup of the heated milk and add to the egg mixture., then add this mixture to the rest of the heated milk. Cook over medium heat, stirring constantly, for about 10 minutes, until thick. Remove from heat.
Add the vanilla and butter and stir. Fold in the coconut. Pur into baked pie crust.
Let cool. When ready to serve, top with whipped cream.