Preheat your oven to 375°F (190°C).

Brush the reserved egg white over the surface of the Oreo crust. (Alternatively, break the crust out of the pan and press it into a tart pan for a different presentation.)

Bake the crust for 5 minutes.

Remove the crust from the oven and let it cool while you prepare the custard.

In a medium saucepan, combine the sugar, cornstarch, and salt.

In a separate bowl, whisk together the milk and egg yolks until smooth.

Gradually pour the milk mixture into the saucepan, whisking constantly to avoid lumps.

Place the saucepan over medium heat and cook, whisking frequently, until the mixture starts to thicken.

Once it thickens, reduce the heat to low and simmer while stirring constantly until the custard is fully thickened.

Remove the saucepan from heat and immediately whisk in the bittersweet chocolate, semisweet chocolate, unsalted butter, and vanilla extract. Stir until smooth and fully combined.

Transfer the custard to a bowl. Press a piece of plastic wrap directly onto the surface of the custard to prevent a skin from forming.

Refrigerate the custard until it is completely cool, about 1–2 hours.

Top the pie with Cool Whip Extra Creamy, spreading it generously over the custard.

Garnish with bittersweet chocolate shavings for an elegant finish.

Chill the pie until ready to serve.