Chocolate milk:

1. Prepare the chocolate milk for soaking by gently warming the milk and whisking in Nutella until completely smooth. Transfer to a shallow dish and let it cool to room temperature.

Nutella mascarpone filling 

1. Make the Nutella–mascarpone base by folding together room-temperature mascarpone and Nutella with a spatula. Mix gently until smooth and uniform, being careful not to overmix.
2. Whip the heavy cream and sugar in a chilled bowl until soft peaks form. The cream should hold its shape but still curl slightly at the tips.
3. Gently fold the Nutella–mascarpone mixture into the whipped cream using a spatula.
4. Fold just until combined and no white streaks remain, being careful not to deflate the cream.

Assemble

1. Quickly dip each ladyfinger into the cooled chocolate milk, spending only 1-2 seconds per side to prevent them from becoming too soggy.
2. Arrange the first layer of dipped ladyfingers in a single, tight layer at the bottom of your dish.
3. Spread a thin layer of melted pure Nutella evenly over the arranged ladyfingers.
4. Spoon half of the prepared tiramisu cream over the Nutella layer and spread it into an even, smooth layer.
5. Add a second layer of quickly dipped ladyfingers over the cream, arranging them neatly.
6. Top with the remaining tiramisu cream, spreading it evenly and smoothing the surface with your spatula.

Refrigerate and Decorate

1. Cover the tiramisu and refrigerate for at least 6-8 hours, or preferably overnight, to allow the flavors to meld and the dessert to set firmly.
2. Before serving, gently warm the remaining Nutella and mix it with chopped hazlenuts and  cover the set tiramisu..
3. For clean, professional-looking slices, place the tiramisu in the freezer for 20-30 minutes before cutting with a sharp knife.