Preheat your oven to 350°F (175°C). Crush the Oreo cookies in a food processor until they form fine crumbs. In a mixing bowl, combine the crumbs with melted unsalted butter, mixing until fully blended. Press this mixture firmly into the bottom of a 9-inch springform pan to create a solid crust. Bake for 10 minutes until set, then let it cool.

In a large mixing bowl, beat the softened cream cheese with granulated sugar and sour cream using an electric mixer on medium speed until smooth and creamy. Add the eggs one at a time, making sure to mix well after each addition to incorporate air. Gently fold in the peanut butter and chopped Butterfinger pieces until evenly distributed for a delectable filling.

Pour the creamy Butterfinger cheesecake filling over the cooled Oreo crust, spreading it evenly with a spatula. Tap the pan lightly on the counter to remove any air bubbles that may be trapped within the batter, ensuring a silky texture throughout.

Create a water bath by placing your springform pan in a larger baking pan filled with hot water reaching halfway up the sides of the cheesecake pan. Bake in the preheated oven for about 50-60 minutes, or until the center is set but still slightly jiggly.

Once baked, turn off the oven and crack the oven door open, allowing the cheesecake to cool gradually for about 1 hour. After cooling, transfer the cheesecake to the refrigerator and chill it for at least 4 hours or preferably overnight.

To create the luscious chocolate ganache, heat 1 cup of heavy cream in a saucepan until it simmers. Pour over 8 ounces of chopped chocolate, letting it sit for 5 minutes before whisking until smooth and glossy. For the whipped cream, whip the remaining heavy cream with powdered sugar and vanilla extract until stiff peaks form.

Remove the chilled cheesecake from the springform pan and place it on a serving plate. Drizzle the chocolate ganache generously over the top, allowing it to drip down the sides. Finally, pipe or dollop the whipped cream around the edges and sprinkle additional chopped Butterfinger pieces on top.