• Preheat the oven to 350F (180C) degrees and position the oven rack in the lower third of the oven.
• Wrap the outside of a 9-inch (23-cm) springform pan with an oven bag or slow cooker liner. Tie the side tight using a key lock tie, if included with the oven bag. Then wrap the outside of the pan with aluminum foil at least 3 times so that the bottom and sides are covered. Ensure that each seam is covered at least once.

Oreo Crust

• Add the Oreos to a food processor and pulse until they're crumbs. Alternatively, place in a freezer bag and crush with a rolling pin.
• Mix together the Oreo cookies and melted butter. You can either do this in a bowl with a fork, or add the melted butter to the cookie crumbs in the food processor and pulse a few times.
• Press the mixture into the bottom of the springform pan creating a slight lip around the edge.
• Bake in the preheated oven for 10 minutes. Remove from the oven and keep the oven turned on.

Cheesecake Filling

• In a very large bowl, beat the cream cheese and sugar until soft and creamy. Turn off the mixer and scrape down the sides and bottom of the bowl periodically to ensure you don't have any lumps.
• Mix in the Nutella and sour cream until smooth. Again, turn off the mixer and scrape down the sides of the bowl periodically.
• Ensure your eggs are whisked together first. Then whisk the eggs into the batter about ½ at a time. Do this by hand using a wire whisk.

Baking & Cooling the Cheesecake

• Place the springform pan (still wrapped in aluminum foil) in the middle of a large roasting pan.
• Pour the cheesecake batter into the pan and smooth the top.
• Pour the boiling water into the roasting pan so that there's about ½ - 1 inch of water in the roasting pan.
• Place the entire thing in the oven to bake for about 50-60 minutes, or until the top looks just set, but there's still a wobble in the middle of the cheesecake.
• Remove the water bath from the oven and gently trace around the outside of the cheesecake with a thin sharp knife.
• Cool the cheesecake in the water bath until it's room temperature, then lift the springform pan out of the roasting pan. Cover the cheesecake with foil and place in the fridge to chill for at least 6 hours or overnight.

Nutella Glaze

• Measure out the Nutella and place in a heatproof glass bowl.
• Heat the cream until hot but not starting to boil. This can be done in a double boiler over low heat or in 30 second intervals in the microwave.
• Pour the hot cream over the Nutella and whisk until smooth.
• Take the cheesecake out of the fridge. Trace around the edges of the cake with a thin, sharp knife, then unclamp the outer ring of the springform pan. If there is condensation on top of the cheesecake, blot it off with a paper towel.
• Pour the Nutella glaze over top of the cheesecake, letting it drip off the edges. Optionally, sprinkle around the edges with hazelnuts. Return the cheesecake back to the fridge until ready to serve.