For the Crust

1. Preheat the oven to 350°F. Spray a 9-inch square pan with cooking spray then line the bottom and sides with parchment paper.
2. Grind the Oreo cookies into a fine crumb using a food processor or blender. In a medium-sized bowl, combine the Oreo crumbs with the melted butter and stir until well combined. Press into the prepared pan.

For the Filling

1. Chop the chocolate bar into small pieces. Melt the chocolate in the microwave in 30-second increments, stirring each time until the chocolate is melted and smooth. Set aside to cool. 
2. In a mixing bowl, beat the cream cheese, sugar, and cocoa powder until well combined and free of any lumps, scraping down the bowl as needed.
3. Next, beat in the eggs, vanilla, and sour cream just until combined. Finally, add the melted chocolate and beat until all ingredients are well combined. Pour the batter over the prepared crust and spread evenly.
4. Bake at 350°F for 15-18 minutes. The centers of the cheesecake should be slightly giggly. Remove from the oven and cool completely in the pan. Then refrigerate for a minimum of 2 hours prior to serving. Keep stored in the refrigerator in an airtight container. Add toppings prior to serving.

For the topping: 

1. Prepare the whipped cream. Place the mixing bowl and whisk attachment in the freezer for 5 to 10 minutes to chill. Pour the heavy whipping cream into the chilled bowl and use an electric mixer to beat the heavy cream on medium-high speed until soft peaks start to form. Slowly add the powdered sugar, cocoa powder, and vanilla extract and continue beating on high speed until stiff peaks form. Pipe or spoon onto the chilled cheesecake and top with fresh fruit.