Preheat oven to 325°F.
In a microwave-safe bowl, add ¼ cup of the heavy cream and the chocolate chips. Heat for 20-second intervals until the chips have melted and the mixture is smooth with no lumps. Set aside.
In a large mixing bowl, beat the cream cheese with a hand-held mixer until creamy and smooth.
Beat in the sugar and cocoa powder until smooth.
Add the eggs, one at a time, and the remaining ¼ cup heavy cream, mixing until combined.
Fold in the melted chocolate mixture. Add the vanilla and stir to combine.
Pour the batter on top of the Oreo crust.
Bake at 325°F for 55-60 minutes. The cheesecake bars are done when the sides are set but the center is still a little bit jiggly.
Remove the cheesecake from the oven and let it rest until the pan is cooled.
Refrigerate for 2-3 hours or until completely chilled.