01 - Preheat oven to 325°F. Wrap the outside of a 9-inch springform pan tightly with aluminum foil to create a waterproof seal and prevent leaks during baking.
02 - Pulse 28 Oreo cookies in a food processor until fine crumbs form. Transfer to a bowl and mix thoroughly with melted butter until all crumbs are evenly coated. Press the mixture firmly and evenly into the bottom of the prepared pan. 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 together until completely smooth and free of lumps, scraping the bowl as needed.
04 - Add the melted and cooled dark chocolate along with the cocoa powder to the cream cheese mixture. Beat until fully combined and uniform in color.
05 - Blend in the sour cream and vanilla extract just until incorporated. Add the eggs one at a time, mixing on low speed after each addition. Stop mixing as soon as each egg is blended in to avoid incorporating excess air.
06 - Gently fold the roughly chopped Oreo cookies into the batter by hand using a spatula, distributing them evenly without overworking the mixture.
07 - Pour the filling over the cooled crust and smooth the top with a spatula. Bake for 45 to 50 minutes until the center is just set with a slight jiggle remaining. Turn off the oven, crack the door open, and let the cheesecake cool inside for 1 hour.
08 - Remove the cheesecake from the oven and allow it to cool completely to room temperature. Refrigerate for at least 4 hours, preferably overnight, until fully set.
09 - Heat heavy cream in a small saucepan until just simmering. Remove from heat immediately and pour over the chopped dark chocolate in a heatproof bowl. Let sit undisturbed for 2 minutes, then stir gently 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.