• Preheat the oven to 350F (180C or 160C in a fan-forced oven).
• Wrap the outside of a 9-inch (23-cm) springform pan with tin foil. Wrap the pan at least 3-4 times so that the bottom and sides are well covered, and all the seems are covered.

Oreo Crust

• Crush the Oreos (wafers and filling) in a food processor until fine crumbs. Or place in a freezer bag and bash with a rolling pin.
• Mix the crushed cookies with the melted butter.
• Press the mixture into the bottom of the prepared pan, creating a slight lip around the edge.
• Bake in the preheated oven for 8-10 minutes. Remove from the oven, leaving the oven turned on.

Cheesecake

• Finely chop the dark chocolate and place in a heatproof bowl.
• Heat the cream until almost boiling.
• Pour ½ cup of the cream over the chopped chocolate. Let sit for 2-3 minutes, then whisk until smooth. If the chocolate isn't quite melted, microwave on medium power for 30-second intervals until smooth. Set aside.
• Whisk the instant coffee powder into the remaining ½ cup of hot whipping cream. Set aside.
• In a very large bowl beat the cream cheese until smooth (about 2 minutes). Beat in the sugar and cornstarch until combined. Turn off the mixer and scrape down the sides of the bowl to ensure there are no lumps.
• Beat in the eggs 1 at a time, turning off the mixer and scraping down the sides in between each addition. Stop mixing as soon as you no longer see pieces of egg yolk or egg white.
• Divide the batter in half.
• Whisk the melted chocolate mixture into 1 half of the batter. Whisk the instant coffee powder dissolved in cream into the 2nd bowl of the batter.

Baking & Cooling

• Place the springform pan (still wrapped in foil) in the middle of a large roasting pan.
• Pour the chocolate cheesecake batter on top of the crust and smooth the top.
• Carefully spoon the coffee cheesecake batter on top of the chocolate layer so that it's evenly covered.
• Pour boiling water into the roasting pan so that there's about 1 inch of water in the roasting pan.
• Place the large roasting pan (with the cheesecake inside) in the oven. Bake for 50-65 minutes, or until the top looks almost set and the cheesecake wobbles slightly (think like pudding or jello) if you gently nudge the pan.
• Remove the roasting pan from the oven. Cool the cheesecake in the pan until it's room temperature.
• Remove the springform pan from the roasting pan. Cover the cheesecake with foil and place in the fridge to chill for at least 6 hours, or overnight.

Ganache, Whipped Cream & Serving

• After the cheesecake has chilled for at least 6 hours, remove from the fridge. Trace around the outside with a thin, sharp knife. Then unclamp the outer ring of the springform pan. If there's any condensation on top of the cheesecake, use a paper towel to blot it off.
• For the ganache, chop the chocolate into very fine pieces and place in a heatproof bowl.
• Heat ½ cup cream until almost boiling. Pour the cream over the chocolate. Let sit for 2-3 minutes, then whisk until smooth.
• Pour the ganache over the top of the cheesecake. Use a flat knife to spread it to the edges, if needed. Return to the fridge for the ganache to firm up.
• For the coffee whipped cream, beat the cream and instant coffee powder until stiff peaks form. The instant coffee powder will dissolve as you whip the cream.
• Transfer the whipped cream to a piping bag with a piping tip (I used a Wilton 1M) and pipe rosettes around the edges of the cheesecake.
• Slice the cheesecake with a sharp, thin knife (not a table knife). Be sure to cut all the way through the crust. For clean cuts, wipe off the knife after each slice.