Prep: Preheat oven to 350° F. Spray a 9 inch springform pan with nonstick spray and make sure the bottom is securely fastened. You can line the bottom with parchment paper (it will stick out through the bottom) for easy removal post-bake.
Make the Crust: Stir together crust ingredients and press into prepared pan and up the sides a bit (see photos above). Bake this for 10 minutes. Set aside. Keep the oven on at 350. Fill a large pot with water and set it on your stove, and get out a large roasting pan – you'll need this for your water bath later.
Make the Cheesecake Filling: Remember that your cold ingredients need to come to room temp before you start. In a large mixing bowl, cream softened cream cheese until creamy, about 1-2 minutes. Add the sugar & mix until just incorporated. Scrape the sides of the bowl with a rubber spatula as you go. Add the eggs one at a time, mixing on medium speed after each until just incorporated. Add the vanilla and sour cream, and mix until just incorporated. Add the nutella last, mixing on medium speed until just incorporated.
Bake: Bring the large pot of water to a boil. Set your springform pan on a rack positioned in the center of the oven, and place the roasting pan on the rack below, or wrap the base of the cheesecake pan in foil and place it inside a 10-inch cake pan inside the roasting dish. Pour the boiling water into the roasting pan. Both of these methods ensure no leaks.Bake for 1 hour 32 to 1 hour 45 minutes. When done, the cheesecake will have only a slight wobble in the center, and a knife inserted into the edge will come out clean, and will have a bit of thick batter when inserted into the center.Turn off the oven and crack the door open. Let the cheesecake cool in the oven for 1 hour before removing it.
Cheesecake Cooling: Once the hour is up, remove the pan from the oven. Remove foil and set the springform pan on a wire rack. Let cool completely at room temp, then cover with foil and refrigerate at least 6 hours or up to 1 day before removing from the pan and serving.
Make the Ganache: Add nutella to a heatproof bowl. Heat heavy cream in a small saucepan over medium heat until simmering. Pour over the nutella and let rest 30 seconds, then stir until completely smooth. Let cool to room temperature before adding to the cheesecake.
Make the Whipped Cream: If you want to pipe this, you'll need to stabilize it – see note below. Add the nutella and 3 tbsp heavy cream to a medium bowl with the powdered sugar and vanilla extract. Beat on medium high speed until combined, then beat for 1 minute on high speed. Add the remaining heavy cream and beat on medium high speed until stiff peaks form.
Serve & Store: Pour the room temperature ganache over the chilled cheesecake and top with whipped cream. Slice and enjoy! Store leftovers in an airtight container in the fridge for 3-4 days.