Prepare the crust: Preheat your oven to 350°F (175°C). In a mixing bowl, combine the chocolate cookie crumbs and melted butter. Mix until fully combined. Press the mixture firmly into the bottom of a 9-inch springform pan to form an even layer for the crust. Bake for 10 minutes, then let cool.
Make the filling: In a large mixing bowl, beat the softened cream cheese with a hand mixer or stand mixer until smooth. Gradually add granulated sugar and continue beating until well combined and fluffy.
Add flavors: Mix in the hazelnut spread, cocoa powder, and vanilla extract until smooth. Then add the eggs, one at a time, beating well after each addition. Finally, stir in the heavy cream until fully incorporated.
Combine hazelnuts: Gently fold in the chopped toasted hazelnuts into the cheesecake batter, reserving some for topping.
Pour and bake: Pour the cheesecake filling over the cooled crust in the springform pan. Smooth the top with a spatula. Bake in the preheated oven for about 45-50 minutes, or until the edges are set and the center slightly jiggles.
Cool: Turn off the oven and crack the door ajar, allowing the cheesecake to cool slowly for about one hour. Afterward, transfer to the fridge and chill for at least 4 hours, ideally overnight.
Serve: Release the cheesecake from the springform pan, dust with powdered sugar, and top with the reserved hazelnuts. Cut into slices and serve chilled.