01 - Preheat oven to 325°F. Wrap the outside of a 9-inch springform pan tightly with aluminum foil to create a waterproof seal, preventing any water bath leaks during baking.
02 - Pulse 28 Oreo cookies in a food processor until fine, uniform crumbs form. Transfer to a bowl and combine thoroughly with the melted butter. Press the mixture firmly and evenly into the bottom of the prepared springform pan, creating a compact, level crust. Bake for 10 minutes, then set aside to cool slightly.
03 - Using an electric mixer on medium speed, beat the softened cream cheese and granulated sugar until completely smooth and free of lumps, approximately 2 to 3 minutes. Scrape down the bowl as needed.
04 - Add the melted and cooled dark chocolate along with the unsweetened cocoa powder to the cream cheese mixture. Beat on medium speed until fully combined and the batter is uniformly rich in color.
05 - Blend in the sour cream and pure vanilla extract, mixing just until incorporated. Avoid overmixing at this stage to prevent excess air in the batter.
06 - Add the eggs one at a time, mixing on low speed after each addition just until the yolk disappears. Gently fold in the 8 chopped Oreo cookies by hand using a spatula, distributing them evenly throughout the batter without overworking it.
07 - Pour the filling over the cooled crust and smooth the top with a rubber spatula. Bake for 45 to 50 minutes until the edges are set and the center still has a slight jiggle. Turn off the oven, crack the door open, and let the cheesecake rest inside for 1 hour to prevent cracking.
08 - Remove the cheesecake from the oven and allow it to cool completely to room temperature. Transfer to the refrigerator and chill for at least 4 hours, preferably overnight, for the best texture and clean slicing.
09 - Heat the heavy cream in a small saucepan until it just begins to simmer. Remove from heat immediately and pour over the finely chopped dark chocolate in a heatproof bowl. Let sit undisturbed for 2 minutes, then stir gently from the center outward until a smooth, glossy ganache forms. Pour over the chilled cheesecake and spread evenly. Sprinkle crushed Oreos on top if desired. Refrigerate for 30 minutes before slicing and serving.