Using a hand mixer or a stand mixer fitted with the whisk attachment, combine melted butter, sugar, eggs and vanilla extract. Mix until combined.
Add in dry ingredients (cocoa powder, flour, baking powder, salt). Mix until combined.
Add in mini chocolate chips. Mix until combined.
Grease a 9-inch spring-form pan and cover the outside of the pan with aluminum foil.
Evenly pour the batter into the pan. Bake for 15-20 minutes or until a toothpick comes out partially clean (no wet batter, but with crumbs attached).
Remove from oven, set aside to cool. Leave the oven on.
To make the peanut butter cheesecake
Add water bath to oven. *See Notes for more information.
Using a hand mixer or a stand mixer fitted with the paddle attachment, beat the cream cheese until smooth.
Add in heavy cream, sugar, peanut butter, vanilla extract and salt. Mix well.
Add in eggs and mix until just combined. (Do not over beat)
Add in mini chocolate chips. Mix until combined.
Spread the batter evenly over the brownie bottom. Bake for 30-45 minutes or until there is only a 1-2 inch jiggle in the center. Turn off oven, but leave cheesecake in the oven.
Remove cheesecake from the oven after 45 minutes and let it cool to room temperature.
Place in the fridge for 4-6 hours or overnight to set before adding toppings.
To make the peanut butter frosting
Using a hand mixer or a stand mixer fitted with the paddle attachment, beat the cream cheese and butter until smooth.
Add peanut butter and vanilla extract. Mix until combined.
Add powdered sugar, ½ to 1 cup at a time, mixing in between each addition.
Add heavy cream, ½ tablespoon at a time, until the frosting has reached the desired consistency (usually around 2 tablespoons total). Mix between each addition.
Set the frosting aside.
To make the ganache topping
Heat the heavy cream in a small saucepan on low to medium heat, stirring every 30 seconds.
Heat the cream until it just starts to boil, then turn off heat and add the chocolate. Stir constantly until all of the chocolate has melted. Turn heat back on low if necessary (while constantly stirring) to ensure all of the chocolate is melted.
Let the chocolate cool for 5-10 minutes, then spread evenly over the top of the chilled cheesecake. Place cheesecake back in the refrigerator for 1-2 hours or until the ganache sets.
Once the ganache has set, prepare a piping bag fitted with a star attachment and fill it with the peanut butter frosting. Pipe the frosting on the cheesecake as desired (I piped swirls that outlined where each piece would be cut - see photos above).
Notes
*A water bath is simply a pan of hot water that is placed in the oven while baking. It adds moisture to the oven and helps to keep your cheesecake from cracking. A water bath also provides a more even bake.