CRUST:
Place the Oreo cookies into your food processor and pulse until crumbly. Melt the butter and add it to the cookies. Pulse until this is thoroughly combined.
Press this crust into a springform pan, covering the bottom and going a little up the sides. You may use the bottom of a glass to press the crumbs down.
Place the crust in the fridge while you are making the filling.
TO MAKE THE FILLING:
In a heavy large saucepan, whisk together the sugar, cornstarch, and cocoa.
In a separate large mixing bowl, whisk together the half and half and the egg yolks. Gradually add this mixture to the saucepan, whisking constantly. When this mixture is smooth, turn the heat on to medium high. Whisk constantly as this begins to bubble. Turn the heat down to medium and simmer this mixture for another minute. Make sure you are constantly scraping the bottom and sides.
Remove the saucepan from the heat. Add the butter, chocolate, and vanilla. Stir until smooth.
Pour this mixture into the chilled crust. Place plastic wrap onto the pie and place in the fridge for at least 6 hours.
While the pie is cooling make the whipped cream.
Whipped Cream:
Place the cold heavy cream into a cold standing mixer bowl. Add the powdered sugar and vanilla. Beat this until peaks form. Add the cornstarch and continue beating until the peaks are stiff.
Add the whipped cream to the top of the chilled pie.
