Preheat oven to 350°F. Line the bottom of a 9-inch springform pan with parchment and lightly grease the sides.
Melt the butter in a saucepan, remove from heat, and whisk in both sugars until combined and glossy.
Whisk in the eggs and vanilla until smooth.
Stir in cocoa powder, flour, and salt until fully incorporated.
Fold in chopped Oreos, then spread the brownie batter evenly in the prepared pan.
Bake for 22–25 minutes or until the center is just set. Let cool completely in the pan.
Beat softened cream cheese, granulated sugar, and vanilla extract in a large bowl until smooth and creamy.
In a separate bowl, whip heavy cream and powdered sugar until stiff peaks form.
Fold the whipped cream into the cream cheese mixture until well combined and fluffy.
Stir in the crushed Oreos, then spoon the cheesecake mixture over the cooled brownie layer.
Smooth the top and chill in the fridge for at least 6 hours or overnight until firm.
Whip the heavy cream and powdered sugar for the topping until stiff peaks form, then gently fold in the finely crushed Oreos.
Transfer the Oreo whipped topping to a piping bag fitted with a star tip and pipe swirls around the edges.
Decorate with mini Oreos on top of the piped swirls before serving.