To make the Oreo crust: Preheat the oven to 325°F (163°C). Add the Oreos to a blender or food processor and process until you have fine crumbs. Scoop the crumbs into a mixing bowl and add the melted butter. Mix together until all of the crumbs are moistened.
Scoop the mixture into a 9-inch springform pan and firmly press it down into an even layer on the bottom of the pan.
Bake at 325°F (163°C) for 8 to 10 minutes, then remove from the oven and set aside to cool slightly while you make the filling.
To make the cheesecake filling: Set a large pot of water to boil for the water bath before getting started with the filling. Alternatively, heat water in a kettle or hot water boiling device.
Add the chopped semisweet chocolate to a microwave-safe bowl.
Heat in the microwave in 20 second intervals, stirring in between each one, until the chocolate is completely melted and smooth. Whisk in the espresso powder and set aside.
In the bowl of a stand mixer fitted with the paddle attachment, or in a large mixing bowl using a handheld mixer, beat the cream cheese, sugar, and cocoa powder on medium speed until smooth and well combined. Scrape down the sides of the bowl.
Add the sour cream, heavy cream, vanilla, and salt and mix until fully combined, stopping to scrape down the sides of the bowl as needed. Mix in the melted chocolate on medium speed until no lumps remain and the mixture is completely smooth, then mix in the eggs on low speed until just combined.
To bake the cheesecake: Wrap the cooled springform pan with the pre-baked Oreo crust in 2 layers of aluminum foil, then place into a large oven bag. Fold the oven bag down the sides of the springform pan.
Pour the cheesecake filling into the springform pan and smooth it out into one even layer. Tap the pan on the counter a couple of times to bring any air bubbles to the top, then use a toothpick or skewer to remove any large air bubbles and smooth them out.
Carefully place the wrapped springform pan into a large roasting pan or 12” cake pan with high sides.
Place the pan into the oven on the middle rack. With the rack pulled out, carefully and slowly add the boiling water you started before the filling into the roasting pan until it is about 1-inch deep.
Bake at 325°F (163°C) for 65 to 70 minutes or until the edges of the cheesecake are set and the center is still slightly jiggly. Turn the oven off, crack the oven door slightly, and allow the cheesecake to cool in the warm oven for 1 hour.
After the cheesecake has cooled for 1 hour in the oven, remove it from the oven and transfer to a wire rack to cool completely. Once cooled, cover tightly with plastic wrap or aluminum foil and transfer to the refrigerator to chill for 5 to 6 hours or overnight.
Run a thin knife around the outside of the cheesecake to loosen it from the pan, carefully release the springform pan, then slice into pieces, serve, and enjoy!