Preheat oven to 325 degrees. Spray the sides of the 9-inch springform pan with nonstick baking spray. Wrap the sides of the pan with a strip of parchment paper.
In a food processor, add in the oreo cookies. Pulse until the oreo cookies are a fine crumb. You can also add the cookies into a storage bag and crush the cookies with a rolling pin.
Add the melted butter into the oreo cookie crumbs and pulse a couple of times until the butter is distributed.
Dump the cookie crumbs into the prepared pan. Press the crumbs evenly into the bottom of the pan.
Place the pan into the preheated oven and bake for 10 minutes. Remove from the oven and let cool while you work on the cheesecake filling.
Chocolate Cheesecake Filling
In a bowl, add in the cocoa powder and sugar. Stir to combine. This will prevent lumps of cocoa powder. Set aside.
In a large mixing bowl, add in the cream cheese. Beat using a hand mixer on medium until smooth. Scrape down the sides of the bowl.
Add the cocoa powder and sugar mixture in with the cream cheese. Continue to beat on medium until incorporated. Scrape down the sides of the bowl.
Add the Baileys Irish Cream to the melted semi-sweet chocolate and stir until combined.
Pour the chocolate mixture into the cream cheese mixture and beat until incorporated.
Add in the sour cream and one of the eggs into the cream cheese mixture. Beat until incorporated. Scrape down the sides of the bowl. Add the remaining eggs one at a time until all are incorporated and scrape the sides of the bowl again.
Wrap the bottom of the springform pan with 2 layers of heavy-duty tin foil. Place the cheesecake into a slightly bigger pan and fill with 1 inch of water.
Pour the cheesecake batter on top of the oreo cookie crust.
Place in the oven. Let the cheesecake bake for 1 hour 16 minutes or until done. 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 in the chocolate chips, Baileys, and heavy cream. Microwave for 1 minute and stir until the heavy cream is incorporated. Microwave one more time for 30 seconds and stir until the ganache comes together and is smooth.
Pour the ganache on top of the chilled cheesecake.
In a large mixing bowl, add in the heavy cream. Beat on medium until soft peaks form.
Add in the powdered sugar and Baileys Irish Cream and beat until stiff peaks form.
Add the whipped cream in a piping bag fitted with the 1M tip.
Pipe swirls on the top of the chilled cheesecake to finish it off.