In a medium bowl combine the chocolate cookie crumbs and melted butter.
Press the mixture into the bottom of the spring-form pan and pack it down as well as possible. Chill for 10 minutes in the fridge to set.
Add the vanilla (if desired) and mix to combine.
Cover the pan with plastic wrap and let the cheesecake sit in the freezer for 2-4 hours and then in the fridge overnight. I always find that chilling overnight is best since it help the cheesecake become very firm and helps it slice nicely.
Alternatively, chill in the fridge overnight and then place in the freezer for 2 hours before serving. This will yield the same result.