Line an 8x8-inch baking pan with parchment paper.
Crush the chocolate cookies into fine crumbs.
Mix the cookie crumbs with melted butter.
Press the mixture firmly into the bottom of the prepared pan.
Place in the refrigerator while preparing the filling.
Beat the cream cheese until smooth and creamy.
Add Nutella, powdered sugar, and vanilla extract.
Mix until fully combined.
In a separate bowl, whip the heavy cream until stiff peaks form.
Fold the whipped cream gently into the Nutella mixture.
Spread the filling evenly over the chilled crust.
Smooth the top with a spatula.
Refrigerate for at least 6 hours or overnight.
Drizzle the warmed Nutella over the top.
Sprinkle with chopped hazelnuts.
Slice into bars and serve chilled.