For the crust, combine the 8 tablespoons of melted butter with the crushed Oreo Cookies. Press into a 9.5 inch or 10 inch pie pan. Refrigerate for at least one hour.
Combine the sugar, flour, cornstarch, cocoa powder, salt and in a saucepan. Cook for 1 minute on low-medium heat.
In a separate bowl or container, combine the heavy cream, egg yolks, and vanilla extract.
Whisk the egg mixture into the flour mixture. Continue whisking so that the mixture doesn’t stick to the bottom of the dish as it cooks. Cook until the mixture thickens.
Remove from the heat. Using a wooden spoon, stir in the butter and chocolate. Return the chocolate mixture to low heat and stir for an additional minute or two. Stir until the mixture is smooth.
Pour the mixture into the prepared pie shell.
Refrigerate for at least 1 hour before piping or spooning on the whipped cream frosting. After frosting the pie, refrigerate for at least another hour (or overnight).