Spread the pumpkin puree on a couple of layers of paper towels to get rid of any excess moisture. Let drain for several hours.
Preheat your oven to 350 degrees F. Butter a 9-inch nonstick springform pan. Put a kettle on to heat up some water. You’ll need this for your water bath.
Put the graham crackers, hazelnuts and brown sugar in a food processor fitted with the blade and pulse until the mixture becomes a fine crumb. Drizzle melted butter on top and pulse until just mixed and resembles wet sand. Press the mixture into the bottom of the prepared springform. Place the crust in the center of the oven for 10 minutes or until it starts to turn a little golden. Set aside to cool. Once cooled, spread the chocolate hazelnut spread over the crust, wrap the bottom of the springform pan in two layers of foil and set in the center of a roasting pan.
Increase your oven temperature to 400 F.
Put the cream cheese and granulated sugar in an electric-stand mixer fitted with the paddle attachment and beat on low until smooth. A couple of notes here… First, if you don’t have an electric-stand mixer you can use your beautiful arms and a spatula to beat it into submission. Second, you don’t want to add too much air, at any point, into this creamy mixture. Too much air can make unsightly cracks on your cheesecake. Thus keep it to a low-speed beating as much as possible. Once the cream cheese is smooth, add the salt, cinnamon, cardamom, cloves, ginger and nutmeg. Scrape the pumpkin off of the paper towels and in with the cream cheese mixture. Mix until completely combined taking care to scrape the sides and bottom of the mixing bowl so that everything is incorporated (do this periodically). Add the eggs, one at a time, making sure they are completely blended before adding the next. Lastly, add in the cream and vanilla. If you have any rogue bits that are still in chunks, smash them against the bowl to smooth out or you can pass the mixture through a sieve to eradicate any chunks. Pour the mixture on top of the hazelnut spread and place the roasting pan in the center of the oven.
Pour your boiling water in the roasting pan being careful not to get any water in the springform pan with your cheesecake. Fill to about 1 cm up the side of the cheesecake pan. Should be about 3 to 4 cups of water.
Bake for 15 minutes and then turn the temperature to 250 F and bake for 1 hour more.
When the timer goes off, turn the oven off and let the pumpkin hazelnut cheesecake sit in the oven for 30 minutes, with the door open. Transfer to the counter to cool for several hours more. Once cool to the touch, wrap tightly and place in the fridge until ready to serve.
When ready to serve, take the side of the springform pan off…you may need a knife to gently run along the side. Periodically clean the knife with a damp cloth to keep everything as clean and smooth as possible. Follow this advice when cutting slices. Garnish the top with raw hazelnuts + sea salt flakes.