01 - Preheat oven to 325°F. Tightly wrap the outside of a 9-inch springform pan with heavy-duty aluminum foil, ensuring it extends up the sides to create a waterproof seal against water bath moisture.
02 - Pulse 28 Oreo cookies in a food processor until fine, even crumbs form. Transfer to a bowl and pour in the melted butter, stirring until the mixture resembles wet sand. Press firmly and evenly into the bottom of the prepared pan. Bake for 10 minutes, then remove and let cool while preparing the filling.
03 - Using an electric mixer on medium speed, beat the softened cream cheese and sugar until completely smooth and free of lumps, about 2 minutes. Add the melted and cooled dark chocolate along with the cocoa powder, mixing until uniformly combined and rich in color.
04 - 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 until just combined—do not overmix to prevent cracking. Gently fold in the chopped Oreos by hand using a spatula.
05 - 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 but the center still has a slight jiggle when gently shaken. Turn off the oven, crack the door open, and let the cheesecake rest inside for 1 hour.
06 - 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.
07 - Heat the heavy cream in a small saucepan over medium heat until it just begins to simmer—do not boil. Immediately pour over the chopped dark chocolate in a heatproof bowl. Let sit undisturbed for 2 minutes, then stir gently from the center outward until a glossy, smooth ganache forms.
08 - Pour the ganache over the chilled cheesecake, spreading evenly with an offset spatula. Sprinkle crushed Oreos over the top for garnish. Refrigerate for 30 minutes to set the ganache before slicing and serving.