While baking the oreo brownie, prepare the cheesecake mixture. With the mixer on medium low, beat the cream cheese until there are no clumps.
Next, add in sour cream, flour, eggs, sugar, and vanilla. Mix on medium-low for another 2 minutes.
Then, wrap the bottom of the springform pan with heavy duty foil 3 times to prevent water from entering. Make sure this is tightly wrapped.
Place springform pan in a larger pan and fill with water ⅓ of the way.
Next, pour the cheesecake batter on top of the brownie.
Lastly, place the pan into the oven and bake for 50 mins. The cheesecake should be slightly jiggly in the center with no air bubbles on top when it is finished cooking.
Turn off the oven and crack the door open. Leave the door open for 1 hour to allow the cheesecake to slowly come to room temperature.
Remove the pan from the oven, and let it cool for another 30 minutes on the counter. Remove the springform pan from the water bath, remove the foil, and allow the Oreo brownie cheesecake to cool for 30 more minutes, cover with foil, then place in the fridge for 4-6 hours or overnight. If adding buttercream to the top, do so once the cheesecake has been in the refrigerator for at least 6 hours. If your cheesecake has any condensation on the top, be sure to pat this dry with a paper towel before adding buttercream. To pipe the buttercream on this cheesecake, I used a Wilton 3M piping tip.