Make the Crust: Preheat oven to 350° F. Spray a 9-inch springform pan with nonstick spray and make sure the bottom is securely fastened. Pulse the oreos in a food processor until you have fine crumbs. Stir together oreo crumbs and butter, and press into prepared pan and up the sides a bit. Bake for 10 minutes. Set aside. Keep the oven on at 350.

Make the Cheesecake Filling: Melt the chocolate in a small bowl, in 30 second intervals, stirring between each, until completely smooth. Set aside to cool a bit. In a large mixing bowl, beat the softened cream cheese with electric mixer until creamy, about 1-2 minutes. In a small bowl, whisk together the sugar and cocoa powder. Then, mix this into the cream cheese until well combined and smooth. Add the eggs one at a time, mixing on medium speed after each until just incorporated. Check that the chocolate is still melty and add it to the batter with the vanilla, sour cream, corn starch, and salt. Mix until just combined.

Prepare the Water Bath: Bring the large pot of water to a boil. Set your springform pan on a rack positioned in the center of the oven, and place the roasting pan on the rack below. Pour the boiling water into the roasting pan.

Assemble & Bake Cheesecake: Pour the batter over your prepared crust. Bake the cheesecake for 80 to 88 minutes. When done, the cheesecake will have only a slight wobble in the center. Turn off the oven and crack the oven door open. Let the cheesecake cool in the oven for 1 hour before removing it.

Cheesecake Cooling: Once the hour is up, remove the pan from the oven. Let cool to room temperature, about 1 hour more, then cover with foil and refrigerate at least 6 hours or up to 1 day before removing from the pan and serving.

Make Ganache: Add chocolate to a small bowl. Heat heavy cream in a small saucepan over medium high heat until simmering. Pour over the chocolate, let sit for 4 minutes, then stir until completely smooth. Pour over the center of the cheesecake.

Make Whipped Cream: Add all ingredients to a medium bowl, and beat on high speed with an electric mixer until stiff peaks form. Pipe the whipped cream with a Wilton 4B tip.

Serve + Store: Once whipped cream has been added, slice, and serve! Store leftovers in an airtight container in the fridge for 3-4 days.