In a saucepan, begin warming the milk and heavy cream together on medium low until it has warmed and steam is rising.
Meanwhile, beat the egg yolks, granulated sugar, cornstarch, and salt together in a medium sized bowl until the mixture is a pale yellow color.
Slowly stream about half of the hot milk/cream combination into the whisked eggs combination while whisking constantly to temper the eggs.
Pour the tempered egg mix through a fine mesh strainer back into the saucepan, turn the heat to about medium and whisk constantly as the pudding thickens.
Make sure the pudding thickens further than a regular pudding; it should nearly resemble a paste of sorts.
Remove the pan from the heat, add the vanilla and butter, whisk together until the butter has melted. Transfer the pudding to a small bowl, cover with plastic wrap directly on the surface of the pudding and chill.
The Crust:
Start preheating the oven to 325° F (160° C).
Either zip the graham crackers and vanilla wafers in a food processor or smash them to crumbs in a plastic bag then measure out 1 1/2 cups.
In a medium bowl, stir the crumbs and the melted butter together or combine everything in the food processor.
Pour the crumb mixture into a 9” deep dish pie pan, pressing evenly around starting with the sides and ending with the bottom. Bake the crust for 8 minutes and let cool.
Once the crust has cooled, melt the chocolate with the milk in the microwave for about 30 seconds to 1 minute on 50% power. Stir until smooth.
Pour the melted chocolate into the crust and spread it evenly around the bottom and also up the sides if preferred. Set aside.
Assembly:
Once the pudding has cooled enough (it doesn’t need to be entirely chilled though it can be), spread the pudding into the crust, cover with plastic wrap directly on the surface, and chill in the refrigerator for at minimum 6 hours to overnight before serving.
To Serve:
Whip the 1 cup of heavy cream with the powdered sugar until soft peaks form. Dollop the whipped cream atop the entire pie or individual slices. Sprinkle with shaved chocolate if desired.
Note:
Use any combination of graham crackers and vanilla wafers to equal 1 1/2 cups. Six whole cracker sheets plus 16 vanilla wafers is half and half.