Preheat oven to 350 degrees. Grease a 9.5-inch springform pan with nonstick baking spray. Place a circle piece of parchment paper in the bottom on the springform pan and a strip of parchment paper on the sides of the pan. Wrap the outside of the springform pan in tin foil to prevent the butter from spilling out while it's baking. Set aside.
Add the butter and chocolate chips in a double boiler and melt until smooth. You can make your own double boiler by placing a heat-proof bowl on top of a saucepan that has 1 inch of simmering water in it. Don't let the water touch the bowl.
In a large bowl, add in the melted butter and chocolate, vegetable oil, and both sugars. Whisk to combine.
Add in the vanilla extract and eggs. Whisk for about 1 minute until the batter is lighter in color.
Sift in the cocoa powder, flour, and salt. Stir to combine.
Pour the brownie batter into the bottom of the prepared springform pan.
Place in the preheated oven and bake until set, about 30 minutes. Prepare cheesecake batter while the brownies are baking.
Remove the pan from the oven and reduce heat to 325 degrees.
Add the cream cheese in a large bowl. Beat with a hand mixer on medium until smooth. Scrape down the bowl.
Add in the sugar and vanilla extract and beat until combined.
Add in the vanilla extract and then the eggs one at a time. Beat in each egg completely before adding the next. Scrape down the bowl after incorporating each egg.
Add in the heavy cream and sour cream. Beat just until everything is worked into the batter. Scrape down the bottom and sides of the bowl.
Stir the chocolate chips into the cheesecake batter.
Pour the batter into on top of the brownie crust.
Place the cheesecake inside a slightly larger pan. Then add the two pans inside an even larger pan and fill the largest pan with about 1 inch of water to create a water bath.
Place in the preheated oven and bake for 1 hour and 20 minutes to 1 hour and 30 minutes or until the center of the cheesecake is set up. To make sure the cheesecake is done, gently give it a wiggle. If it slightly jiggles in JUST the middle like jello, then it's done. If it jiggles all over, it needs to bake longer. Turn off the heat and crack the oven door slightly. Let it cool in the oven for 1 to 2 hours until it reaches room temperature and then place in the fridge to chill overnight.
In a microwave-safe bowl, add chocolate chips and heavy cream. Microwave in 30-second intervals and stir after each one. Repeat until the ganache is smooth and completely melted.
Let it sit at room temperature until it thickens to a spreadable consistency. You can speed up the process by placing it in the fridge. Keep an eye on it.
Add the ganache into a piping bag fitted with a 1M tip. Pipe swirls on the top of the cheesecake.