Trace the bottom of the springform pan on a sheet of parchment paper and cut out the circle.
Spray the sides and bottom of the springform pan with nonstick cooking spray. Place the parchment paper in the bottom and spray that as well. Set aside.
Smash the Oreos into small crumbs. You can do this with a food processor. If you don't have a food processor, place the Oreos into a ziplock bag (gallon size is perfect). Seal the bag letting out the air and whack the cookies firmly with a rolling pin. Flip the bag over to be sure you crush all of the cookies.
Place the cookie crumbs in a large bowl. Make sure there aren't any large pieces. You can place them back in the bag and crush them again, if necessary.
Cut the butter into tablespoon sized pieces (doesn't have to be exact) and place in a small heatproof bowl or mug and melt in the microwave.
Stir the melted butter into the crushed Oreos.
Place the Oreo mixture into the bottom of the prepared pan and press down firmly. I like to use the bottom of a dry measuring cup to do this, but you can use the back of a spoon or your hands. Set aside.
Add the cream cheese and powdered sugar to the bowl of a stand mixer fitted with a paddle attachment. Mix on medium speed until creamy and thoroughly combined. You can use an electric hand mixer if that is what you have available.
Mix in the hot chocolate mix and cocoa powder. Blend until combined.
Add in the sour cream and mix until combined. Set aside.
If you have a second bowl for the mixer, you will use it now. Otherwise, transfer the contents of the mixing bowl to a large bowl and set aside.
Fit the whisk attachment onto the stand mixer.
Pour one cup of heavy cream into the bowl of the mixer and beat on medium high speed until stiff peaks form.
Gently fold the whipped cream into the chocolate cream mixture.
Pour the cheesecake mixture onto the prepared Oreo cookie crust.
Use an offset spatula or even the back of a spoon to make an even layer of filling.
Cover the pan in plastic wrap and let it chill in the fridge for at least 8 hours.
When you are ready to serve your cake, run a knife or an offset spatula around the inside of the springform pan to loosen the cake. Pop open the ring and gently lift it away from the cake.
Serve the cake as is or add a bit of whipped cream and a sprinkle of mini chocolate chips.