Preheat oven to 325°F (163°C). Wrap the outside of a 9-inch springform pan tightly in two to three layers of heavy duty aluminum foil, covering the bottom and going up the sides. Lightly grease the inside of the pan.
Pulse whole Oreo cookies in a food processor until fine crumbs form. Mix with melted butter until it looks like wet sand. Press firmly and evenly into the bottom of the pan and slightly up the sides.
Bake the crust for 8 to 10 minutes, then remove and set aside to cool slightly. Leave the oven on.
Stir instant espresso powder into hot water until fully dissolved. Melt semisweet chocolate in the microwave in 30-second bursts, stirring between each, until smooth. Let cool slightly.
Beat softened cream cheese on medium speed until completely smooth. Add granulated sugar and beat until fluffy. Mix in sour cream and vanilla until just incorporated.
Add eggs one at a time, beating on low speed after each addition just until combined. Pour in dissolved espresso, melted chocolate, and cocoa powder. Gently fold with a rubber spatula until uniform with no streaks.
Pour filling over the cooled crust and smooth the top. Place the foil-wrapped pan inside a large roasting pan. Carefully pour hot water into the roasting pan until it reaches about halfway up the sides of the springform pan.
Bake for 55 to 65 minutes, until edges are set and the center still has a slight jiggle. Turn off the oven, crack the door open a few inches, and let the cheesecake sit inside for about an hour.
Remove from the water bath and unwrap the foil. Run a thin knife around the edge to loosen, but leave in the springform pan. Cover loosely and refrigerate for at least 4 hours, preferably overnight.
Heat heavy cream in a small saucepan until it just starts to simmer. Pour over remaining chopped chocolate in a heatproof bowl, let sit for a minute, then stir until smooth and glossy. Let cool slightly to thicken.
Release the cheesecake from the springform pan and set on a serving plate. Pour ganache over the top, letting it drip slightly over the edges. Top with chocolate covered espresso beans if using.