Preheat your oven to 325°F (160°C). Prepare a 9-inch springform pan by greasing the sides lightly.

In a medium bowl, combine the crushed chocolate sandwich cookies with the melted butter. Mix until the crumbs are evenly coated.

Press the cookie mixture firmly into the bottom of the prepared springform pan to create an even crust. Bake in the preheated oven for 10 minutes, then remove and allow to cool slightly.

In a large mixing bowl, beat the softened cream cheese with a hand mixer or stand mixer until smooth and creamy, about 2 minutes.

Add the granulated sugar to the cream cheese and mix until fully combined. Scrape down the sides of the bowl as needed to ensure even mixing.

Pour in the Nutella, sour cream, and vanilla extract. Beat on medium speed until everything is well incorporated and smooth, approximately 2-3 minutes.

In a separate bowl, whip the heavy cream until soft peaks form. Gently fold the whipped cream into the Nutella mixture until no white streaks remain.

Pour the cheesecake filling over the cooled cookie crust, smoothing the top with a spatula.

Bake the cheesecake for 50-60 minutes, or until the edges are set but the center still jiggles slightly. Turn off the oven and crack the door, allowing the cheesecake to cool in the oven for 1 hour.

Once cooled, chill the cheesecake in the refrigerator for at least 4 hours, or overnight for the best texture.

Before serving, melt the semi-sweet chocolate chips in a microwave-safe bowl, stirring every 30 seconds until smooth. Drizzle this over the cheesecake and sprinkle with chopped hazelnuts, if desired.