Preheat oven to 350 degrees. Grease a 9.5-inch springform pan. 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. Add the butter and chocolate chips in the heat-proof bowl and melt until smooth.
In a large bowl, add in the melted butter and chocolate chips, 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.
Sift in the cocoa powder, flour, and salt. Stir to combine.
Pour 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 creamy.
Add in the sugar and vanilla extract and beat until combined.
Add in the eggs one at a time and mix until each egg is incorporated. Scrape down the sides and bottom of the bowl before adding the next egg.
Add in the heavy cream and sour cream. Beat just until everything is worked into the batter.
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 hot water to create a water bath.
Place in the oven and bake for 1 hour and 20 minutes or until the center of the cheesecake is set up. If you gently wiggle the cheesecake the center of the cheesecake should be the only thing jiggling.
Leave the oven door open slightly with the cheesecake still inside for about an hour. Move the cheesecake to the counter and let it cool to room temperature if it's still hot and place in the fridge overnight to firm up and chill.
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.