Prepare the Ganache: You want this to have plenty of time to cool, so making it before the crust is ideal. Combine the chopped chocolate and 3/4 cup heavy whipping cream in a microwave safe bowl. Microwave in 25 second increments stirring each time, until almost all the way melted. Keep stirring until remaining chocolate melts. Set aside to cool.
Prepare the Oreo Crust: Place Oreos in a food processor. Process until a very fine crumb with no chunks. Combine with melted butter and stir until combines. Press the crust mixture firmly into a 9 inch pie pan. Place in the freezer for about 30 minutes.
Prepare the Chocolate Layer: Combine 1 1/3 cups heavy whipping cream, 2 Tablespoons cocoa powder, 2 Tablespoons sugar and vanilla in a mixing bowl. Beat with an electric mixer for several minutes or until stiff peaks begin to form.
Very gently, fold the cooled ganache into the chocolate whipped cream until fully combined and no streaks are noticeable. Spread the mixture into the pie pan with the chilled Oreo crust. Refrigerate for about 4 hours to set.
Prepare Whipped Cream Topping: Once the chocolate layer has set, or just before serving, whichever you prefer, beat the whipped cream topping ingredients together until stiff peaks begin to form. Place the whipped cream in the center of the chocolate layer and spread out to the edges evenly. Garnish with chocolate curls, chocolate sprinkles or chopped Oreos.
Chill the pie until ready to serve.