Preheat your oven to 350°F (175°C).
Prepare the brownie mix according to the instructions on the box. Press the brownie batter into the bottom of a 9-inch springform pan. Bake for 25-30 minutes or until a toothpick inserted into the centre comes out with a few moist crumbs. Let it cool while preparing the cheesecake filling.
In a large bowl, beat the cream cheese and sugar until smooth. Add the vanilla extract and mix until combined.
Add the eggs one at a time, mixing well after each addition.
Stir in the sour cream and heavy cream until smooth.
Pour the cheesecake filling over the cooled brownie crust.
Place the springform pan in a larger baking pan. Fill the larger pan with hot water halfway up the sides of the springform pan. This will prevent the cheesecake from cracking.
Bake for 55-60 minutes or until the centre is almost set.
Turn off the oven and let the cheesecake cool in the oven with the door slightly open for 1 hour.
Remove the cheesecake from the oven and refrigerate for at least 4 hours or overnight.
Once the cheesecake is chilled and set, remove it from the springform pan.
Decorate the top of the cheesecake with chopped cosmic brownies and drizzle with chocolate ganache or fudge sauce.
Slice and serve.