In a small bowl, sprinkle the gelatin in the cold water.
In a large bowl, whisk together the egg yolks, sugar, salt and vanilla. Slowly whisk in the hot milk. Pour the mixture into the top of a double boiler. Stir and cook until the mixture coats the spoon when it's inserted and pulled out. Add the gelatin to the hot mixture, and stir until dissolved.
Pour the custard into a large bowl and refrigerate until it becomes syrupy and thickened, about 1 to 2 hours.
Use an electric mixer in a large bowl to beat the egg whites until stiff. Fold the egg whites and 1 cup of the whipped cream into the chilled mixture. Pour the cream filling into the baked pie crust and spread to the edges.
Top the pie with the remainder of the whipped cream (sweeten it if you'd like), and sprinkle coconut on top (see tips below).
Notes
Additional coconut may be added to the cream's filling, if desired.