To make filling layer base, over medium heat, combine 1/2 cup granulated sugar, salt and cornstarch in a saucepan.  Whisk yolks into sugar mixture.  Slowly add in milk, combining well. Whisk constantly until mixture thickens.   Be careful to not let the mixture burn.

In a medium bowl, melt bittersweet chocolate.  This can be done on a double-boiler on the stove, or in the microwave.  Cook for 1 minute, stir and cook in 30 second increments until melted. 

Pour half of the milk mixture into the melted chocolate.  (Set other half of milk mixture aside for later.) Stir well and add vanilla to combine.  Pour into the prepared pie crust. This forms the black bottom layer.

Mix cold water and unflavored gelatin in a small bowl.  Stir to combine and mix with remaining milk mixture.  Add whiskey.  Stir again and let set for 8 to 10 minutes. 

While whiskey milk mixture is setting, beat egg whites and cream of tartar together in a standing mixer or in a large bowl with a hand-held mixer.  Whip until foam peaks forms.  Add remaining 1/2 cup granulated sugar to egg whites and beat until stiff peaks form. 

Fold 1/3 of whipped egg whites into whiskey mixture.  Stir well to combine. Fold whiskey mixture into remaining egg whites.  Once combined and smooth, pour over chocolate layer in pie crust.  Let set in the refrigerator for 1 hour. 

While pie is setting, combine 1 tsp. unflavored gelatin and 4 tsp. cold water in a small saucepan.  Heat over low heat, stirring constantly, until gelatin dissolves. Let cool slightly.

Using a standing mixer or hand-held mixer, whip heavy cream, powdered sugar, and vanilla until soft peaks form.  Slowly beat cooled gelatin into cream mixture.  Whip cream on high speed until stiff peaks form.  Spread or pipe onto the top of the cooled pie layers.  Garnish with sifted cocoa powder, or shave chocolate.