Preheat oven to 325 degrees and spray a 9" springform pan with non-stick spray. Set aside.
In a medium bowl, add the brownie mix, vegetable oil, water, and egg. Stir about 50 times (batter may be slightly lumpy) and spread into the prepared pan.
Bake for 25 minutes or until a toothpick inserted in the center comes out clean.
While the brownie base is cooking, prepare the peanut butter cheesecake.
In a large bowl, with a hand mixer (or in your stand mixer), mix the cream cheese, sugar, peanut butter, and vanilla until smooth and creamy.
Add the eggs, one at a time, mixing on low between each addition, until just blended. Store in the fridge until the brownie bottom is baking.
Once the brownie bottom is done, pour the cheesecake mixture on top. Spread it evenly with a spatula.
Raise the oven temp to 350.
Bake for approximately 45-50 minutes or until center is almost set. Check it after 35 minutes to see how it's doing. Mine took closer to 50 minutes.
Cool on the counter for a few minutes then transfer to the fridge.
In a microwave safe bowl, add the chocolate chips & peanut butter. Microwave for 30 seconds, then stir. Microwave another 20 seconds or so or until creamy and fully combined. Add to a plastic baggie, then snip the very tip. Drizzle across the cheesecake.