01 - Preheat the oven to 325°F. Lightly grease a 9-inch springform pan and set aside.
02 - Pulse 24 Oreo cookies in a food processor until fine crumbs form. Drizzle in the melted butter and pulse until the mixture resembles wet sand. Press the crumb mixture firmly and evenly into the bottom of the prepared springform pan. Bake for 10 minutes, then remove and let cool completely.
03 - In a large mixing bowl, beat the softened cream cheese and granulated sugar with an electric mixer on medium speed until completely smooth and creamy, about 2 to 3 minutes. Add the cocoa powder and blend until uniformly incorporated. Pour in the melted and cooled chocolate chips, mixing until the batter is rich and silky.
04 - Add the eggs one at a time, mixing on low speed just until each is fully blended before adding the next. Stir in the vanilla extract and sour cream, mixing until smooth. Avoid overbeating to minimize air pockets.
05 - Gently fold the coarsely chopped Oreo cookies into the batter using a rubber spatula. Pour the filling over the cooled crust, spreading it evenly. Tap the pan firmly on the countertop a few times to release any trapped air bubbles.
06 - Bake on the center rack for 45 minutes, or until the edges are set and the center has a slight jiggle. Turn off the oven, crack the door open slightly, and let the cheesecake rest inside for 1 hour to prevent cracking.
07 - Remove the cheesecake from the oven. Run a thin knife around the edge to loosen it from the pan. Allow it to cool to room temperature, then refrigerate for at least 4 hours or preferably overnight before adding the topping.
08 - Heat the heavy cream in a small saucepan over medium heat until it just begins to simmer; do not boil. Remove from heat and pour over the chocolate chips in a heatproof bowl. Let sit for 1 minute, then stir gently until the ganache is smooth, glossy, and completely blended.
09 - Spread the chocolate ganache evenly over the top of the chilled cheesecake. Arrange Oreo halves or sprinkle crushed Oreo pieces over the ganache for garnish. Return to the refrigerator and chill for at least 30 minutes before slicing and serving.