Combine the cookie crumbs and melted butter. Stir well to combine. Press the mixture into the bottom of a 9-inch springform pan.
Bake for 12 to 15 minutes. Allow to cool slightly, and then butter the sides of the springform pan for the cheesecake mixture.
For the filling: In a stand mixer, beat the cream cheese. Scrape down the sides of the bowl several times.
Add in the sugar and beat it some more; scraping down the sides once or twice.
Add the eggs in one at a time, mixing in between each addition, until thoroughly combined.
Mix in the sour cream on slow speed while pouring the hazelnut liqueur into the bowl in a slow stream.
Wrap the bottom of the springform pan with aluminum foil. Scrape the filling onto the chocolate crust in the pan. Wrap the outside of the pan in 3 layers of heavy-duty aluminum foil and put in a larger pan.
Add enough hot water to the outer pan to come up halfway.
Bake for 1 hour. The cheesecake should be set around the edges but still a little jiggly in the middle.
Allow to set up overnight. Run a thin knife around the edge and open the springform pan. Decorate the top of the cheesecake with chocolate drizzles and hazelnuts dipped in chocolate.
