01 - Preheat oven to 325°F. Wrap the outside of a 9-inch springform pan tightly with aluminum foil, ensuring it extends up the sides to create a waterproof seal for the water bath.
02 - Pulse 28 Oreo cookies in a food processor until fine crumbs form. Transfer to a bowl and pour in the melted butter, mixing until the crumbs are evenly moistened. Press the mixture firmly and evenly into the bottom of the prepared springform pan. Bake for 10 minutes, then remove and let cool.
03 - Using an electric mixer on medium speed, beat the softened cream cheese and granulated sugar together until completely smooth and creamy, scraping down the sides of the bowl as needed.
04 - Add the melted (and slightly cooled) dark chocolate and unsweetened cocoa powder to the cream cheese mixture. Beat until fully combined and no streaks remain.
05 - Blend in the sour cream and vanilla extract, mixing just until incorporated. Avoid overbeating.
06 - Add the eggs one at a time, mixing on low speed after each addition just until the yolk disappears. Gently fold in the chopped Oreo cookies by hand using a spatula. Do not overmix, as excess air causes cracking.
07 - Pour the filling over the cooled crust and smooth the top with a spatula. Bake for 45-50 minutes until the edges are set but the center still has a slight jiggle. Turn off the oven, crack the door open, and let the cheesecake cool inside for 1 hour to prevent sinking.
08 - Remove the cheesecake from the oven and allow it to cool to room temperature. Refrigerate for at least 4 hours, preferably overnight, until fully set.
09 - Heat the heavy cream in a small saucepan until just simmering—do not boil. Remove from heat and pour over the chopped dark chocolate in a heatproof bowl. Let sit for 2 minutes, then stir gently from the center outward until a smooth, glossy ganache forms. Pour over the chilled cheesecake and spread evenly. Top with crushed Oreos. Refrigerate 30 minutes before slicing.