Preheat oven to 325°F (163°C). Line a 9-inch springform pan with parchment paper and grease the sides.
Prepare the brownie batter according to package instructions and pour it into the prepared pan. Bake for 25 minutes, then remove and set aside to cool slightly.
In a large mixing bowl, beat the softened cream cheese until smooth. Add sugar and vanilla and beat again until creamy.
Add eggs one at a time, mixing just until combined. Fold in sour cream and mix until smooth.
Pour the cheesecake batter over the brownie base and smooth the top. Bake for 50-60 minutes or until center is set.
Turn off the oven, crack the oven door, and let the cheesecake cool inside for 1 hour. Then remove and refrigerate for at least 4 hours or overnight.
To make the ganache, heat heavy cream until just simmering, then pour over chocolate chips. Let sit for 2 minutes, then stir until smooth.
Pour the ganache over the chilled cheesecake and spread evenly. Refrigerate until set before slicing and serving.