Crust

1. Grease a 9-inch springform pan set aside. Preheat oven to 325F/163C.Prepare graham cracker crust and par-bake for 6-8 minutes, until set and not overly browned.

Cheesecake

1. In the bowl of an electric mixer fitted with a paddle attachment or large bowl with a hand mixer beat the cream cheese for 2 minutes on medium speed. Reduce speed to low and add in Nutella and mix to combine. Add granulated sugar and beat for another 2 minutes. Add in cocoa powder, heavy cream, sour cream, vanilla extract- mixing until fully combined. Add in eggs one at a time, but do not over mix. You should have a creamy batter with no lumps.
2. Pour into prepared pan. Place 9-inch springform pan in a large cake pan or wrap the springform in a thick layer of foil coming up the sides- place cake pan in roasting pan and fill roasting pan with hot water halfway up the sides of the cake pan. This prevents ANY water from getting in the cheesecake and you don't have to wrap everything with foil.
3. Bake for 1 hour and 25 minutes to 1 hour and 15 minutes, the middle of the cheesecake should jiggle just a little bit. Turn oven off and let cool in the oven for 1 hour then take out of roasting pan and place on a wire rack to cool for another hour. Then wrap with plastic wrap and chill in the fridge overnight.

Topping

1. Use an angled spatula to loosen the cheesecake from the springform pan then carefully transfer it to a serving plate. Drizzle melted Nutella on top of cheesecake. Add piped whipped cream and sprinkle on raspberries and toasted hazelnuts. Store in the fridge until ready to eat. 
2. Let sit at room temperature for 15 minutes before serving. Use a knife dipped in hot water then wiped dry each time you slice for clean slices of cheesecake. Store leftovers in an air-tight container in the fridge for up to 5 days.