Grind thin mint cookies into crumbs. Stir together with sugar and melted butter until crumbs are moistened and press into a pie plate. Refrigerate.
In a small pot, stir sugar, cornstarch and cocoa powder together. Whisk in milk and place over medium heat until mixture comes to a boil and starts to thicken.
Once hot and thick remove from heat and stir in chopped chocolate, vanilla and peppermint extract. Pour into pie plate and cover with plastic wrap. Be sure to place the plastic wrap directly on the filling. Refrigerate for 2 hours or until completely chilled and plastic wrap comes off clean.
For the topping, whip cream, powdered sugar, vanilla and peppermint extract together until stiff peaks form. Spread half overtop entire pie and use the remaining to decorate the edges. Top with extra thin mint cookies and serve.