Make the crust: Preheat oven to 375 degrees. In a small bowl, combine graham cracker crumbs and melted butter. Mix until it is well blended and the consistency of wet sand. Add more butter if needed. Press into your pie pan and chill in the freezer for at least 15 minutes to help prevent crumbling when serving. Bake for 8-10 minutes. Let cool before filling.
Make the pudding: In a medium bowl, whisk 2 egg yolks for about 60 seconds until light yellow and increased in volume. Then whisk in cornstarch and about 1/4 cup of the milk until smooth, set aside.
Place the cocoa, 1/2 cup sugar, salt, and remaining 1 3/4 cup milk in a saucepan over medium-high heat. Remove from heat right before the mixture comes to a boil (you should see little bubbles start forming on the sides of the pan). While whisking constantly, slowly and gradually add the hot cocoa to the egg and cornstarch mixture. Pour the combined mixture back into the saucepan. Cook over medium-high heat, whisking constantly, until the pudding comes to a full boil. Reduce heat to a simmer and continue whisking for a few minutes until the pudding has thickened.
Remove from heat and stir in 2 tsp vanilla extract. Pour into your graham cracker crust and press plastic wrap directly on the surface. Refrigerate while you make the marshmallow topping.
Make the topping: Set up a double boiler - a heatproof medium bowl set over a saucepan of simmering water. Add 3 egg whites and the remaining 3/4 cup sugar to the double boiler and whisk the until the whites are warm and the sugar is dissolved, about 3 minutes. Add the cream of tartar and remaining 1/2 tsp vanilla. Beat at medium speed with an electric mixer until firm. Increase the speed to high and beat the mixture until stiff, glossy, and marshmallow-y, about 5 to 7 more minutes.
Pile the marshmallow topping over your pudding mixture. Torch with a kitchen torch before serving. For perfect slices—cut with a knife that has been run under hot water and dried before each cut is made. Refrigerate leftovers (if there are any…).