In a mixing bowl combine the chocolate cookie crumbs with the melted butter, mix well. Press the mixture firmly into a 9 inch pie plate and refrigerate for 30 minutes.
Combine the half and half, sour cream, and chocolate in a saucepan and bring to a boil over medium heat, stirring constantly.
In a mixing bowl, whisk together the sugar, cornstarch, whiskey, and egg yolks. Whisk in the chocolate mixture.
Pour the mixture into a clean saucepan and bring to a boil over medium heat, whisking constantly. Continue to cook the mixture until thickened, 1 – 2 minutes. Let cool.
Pour the chocolate mixture into the prepared pie crust and refrigerate at least 3 hours or overnight.
Whip the cream with the powdered sugar and vanilla until soft peaks form. Spread the whipped cream on top of the pie, dust with cocoa powder and serve.