• Wrap the outside of the springform pan in aluminum foil at least 3-4 times so that the bottom and sides are fully covered. Ensure that all the seams between pieces of foil are covered too.
• Preheat the oven to 350F (180C or 160C on a fan-forced oven).

Oreo Crust

• Place the cookies (wafers and filling) in a food processor and pulse until they're fine crumbs. You can also crush the cookies by placing them in a freezer bag and crushing with a rolling pin.
• Mix the crushed cookies with the melted butter. It should feel like damp sand.
• Press the mixture into the bottom of the springform pan to create a slight lip around the edge.
• Bake in the preheated oven for 8 minutes, then remove from the oven (keeping the oven turned on).

Filling

• Stir together the white sugar, brown sugar, spices and cornstarch in a medium bowl until there are no lumps.
• In a large bowl, beat the cream cheese until soft. Then mix in the sugar mixture until smooth and creamy. Turn off the mixer and scrape down the sides and bottom of the bowl.
• With the mixer on a low speed, beat in the pumpkin and sour cream until evenly combined.
• Then mix in the eggs 1 at a time with a mixer on a low speed. Stop mixing as soon as the eggs are combined.
• Place the pan (still wrapped in foil) in the middle of a large roasting pan. Pour the cheesecake filling over the crust and smooth the top.
• Pour about 1 inch (2 cm) of boiling water into the large roasting pan.
• Place the entire cheesecake in the roasting pan in the oven and bake for about 50-60 minutes, or until the top looks just set. It should still have a slight wobble in the middle when it's done baking, similar to nudging a bowl of Jello.

Cooling and Chilling

• Remove the cheesecake (in the roasting pan) from the oven. Let it cool in the roasting pan until the water is lukewarm. Then remove the cheesecake from the roasting pan (still in the springform wrapped in foil) and cool until it reaches room temperature.
• Cover the top of the pan with foil and place in the fridge to chill for at least 6 hours or overnight.

Chocolate Ganache & Serving

• Chop the chocolate into very fine pieces and place in a heatproof bowl.
• Heat the cream (either in the microwave or small saucepan while gently stirring) until almost boiling.
• Pour the hot cream over the chocolate and let sit for 2-3 minutes. Then whisk until smooth. If the chocolate hasn't quite melted, microwave for 30 seconds on medium power and whisk until smooth.
• Remove the cheesecake from the fridge. Gently trace around the outside of the cheesecake, then unclamp the outer ring of the springform pan.
• If there's condensation on top of the cheesecake, blot it with a paper towel to remove the water.
• Pour the ganache over the cheesecake and spread smooth. Optionally, let the ganache drip over the edges of the cheesecake.
• Return to the fridge for the ganache to set.
• When ready to serve, slice with a sharp, thin, knife - ensuring that you cut all the way through the crust. Wipe off the knife after each slice for clean cuts.