Preheat oven to 177 degrees Celcius, grease a 9-inch springform pan and set aside. Finely crush the cookies in a food processor, add melted butter and blend until it’s all moistened.
Press crumb mixture onto the bottom of the prepared pan and bake for 8 minutes. Remove from the oven and set on a wire rack to cool while making the filling.
To make the filling
Melt bittersweet chocolate and set aside to cool. Mix cream cheese and sugar until smooth, mix in cocoa powder. Add the eggs one at a time, mixing on low speed and do not overbeat it.
Add melted chocolate and mix on low speed to combine. Pour the filling over the crust and smooth the top.
Bake the cheesecake until the centre is set and the top looks dry (about 1 hour to 1 hour 10 minutes). Cool on a wire rack for 5 minutes, then run a thin knife around the sides of the pan and set the cake in the refrigerator (uncovered), for at least 8 hours, or better overnight.
To make the topping
In a medium saucepan stir together cream, chocolate and sugar on low heat until the chocolate is completely melted and the mixture is smooth.
Cool and pour over the cheesecake. When the topping is set and cooled again run a thin knife around the sides and remove the springform pan sides.
This cheesecake can be prepared up to 2-3 days in advance just store covered in the refrigerator. Garnish with chocolate curls (optional).