Preheat oven to 350°F. Place Oreo cookies in a food processor and pulse until fine crumbs form.
Pour crumbs into a mixing bowl, add melted butter and stir until butter is absorbed.
Transfer mixture to a 9-inch pie plate and press the crumbs into the sides and bottom of the plate.
Bake crust for 10 to 12 minutes, completely until fragrant. Cool.
Place egg yolks in bowl and set aside. Whisk together sugar, cornstarch, cocoa powder and salt. Whisk in the milk, then place the saucepan over medium heat and cook until simmering, stirring occasionally.
Take ¼ cup of the hot mixture and whisk it into the bowl with the egg yolks (this will temper them so they don’t scramble). Pour the egg yolk mixture into the saucepan of simmering milk and continuously whisk until thickened, about 30 seconds.
The mixture should look like this.
Remove pan from heat and add chopped chocolate, butter and vanilla. Use a rubber spatula to stir until melted.
Pour the mixture into prepared pie crust and use an off-set spatula to smooth the top. Cover with plastic wrap and press down so the wrap is touching the filling. Chill for 8 hours or overnight.
Prepare the whipped cream topping and top the pie with the topping. Enjoy!