Start by preheating your oven to 350°F. Grease a 9-inch springform pan and line the bottom with parchment paper to ensure the brownie layer doesn’t stick. In a large bowl, combine the brownie mix, oil, water, and eggs, stirring until fully blended. Spread the batter evenly in the prepared pan and bake for about 15 minutes, just until the top sets slightly. Remove it from the oven and set aside while keeping the oven on for the next layer.

In a mixing bowl, beat softened cream cheese until it’s smooth and fluffy. Add sugar, flour, vanilla extract, sour cream, and heavy cream, mixing until everything is well incorporated. Finally, add the eggs one at a time, gently folding them in to avoid introducing air bubbles. Pour the cheesecake batter over the baked brownie base, smoothing it out evenly.

Reduce the oven temperature to 325°F. Bake the brownie cheesecake for around 45 minutes. Once baked, turn off the oven and let it cool inside with the door closed for 20 minutes, then crack the door open for an additional 30 minutes. This gradual cooling process prevents cracks and ensures a creamy texture.

Once cooled, refrigerate the cheesecake for at least 2 hours or overnight for the best texture. Whip the heavy cream with powdered sugar until stiff peaks form, then spread or pipe it over the chilled cheesecake. Finish by drizzling hot fudge sauce or chocolate ganache just before serving.