Prepare the Oreo Crust:

1. Preheat oven to 350°F (175°C).
2. Crush Oreos in a food processor until fine crumbs form. Stir in melted butter.
3. Press mixture evenly into the bottom and sides of a 9-inch pie dish.
4. Bake for 10-12 minutes. Let cool completely. (Can be made 1-2 days ahead.)

Make the Chocolate Filling:

5. In a medium saucepan, whisk together sugar and milk over medium heat until it starts to simmer.
6. In a separate bowl, whisk egg yolks and cornstarch until smooth.
7. Temper the eggs: Slowly add a few spoonfuls of the hot milk mixture into the eggs, whisking constantly. Repeat a few times.
8. Combine mixtures: Slowly pour the egg mixture back into the saucepan, whisking continuously.
9. Continue cooking, whisking constantly, until the mixture thickens and starts to gently boil (large bubbles breaking the surface).
10. Remove from heat and stir in butter, chocolate, and vanilla until smooth.

Chill the Pie:

11. Pour the chocolate filling into the cooled Oreo crust and smooth into an even layer.
12. Place a piece of plastic wrap directly on top to prevent a skin from forming.
13. Refrigerate for 4-6 hours or overnight until fully set.

Make the Whipped Topping:

14. Once the pudding is set, beat heavy cream in a mixing bowl on high speed for 1-2 minutes.
15. Add powdered sugar and vanilla and continue mixing until soft peaks form (2-3 minutes).
16. Spread whipped cream over the pie and garnish with chocolate curls or shavings.