Preheat oven to 350°F. Line an 8x8 pan with parchment paper, leaving an overhang for easy removal.
Melt the butter in a saucepan, remove from heat, and whisk in both sugars until well combined.
Whisk in the eggs and vanilla until the mixture looks glossy and smooth.
Stir in cocoa powder, flour, and salt until just combined.
Fold in the chopped Oreos, then pour the batter into the prepared pan and spread evenly.
Bake for 22–25 minutes or until the center is set with a slight jiggle. Let cool completely in the pan.
Beat the softened cream cheese, granulated sugar, and vanilla in a bowl until smooth and creamy.
In a separate bowl, whip the heavy cream and powdered sugar until stiff peaks form.
Gently fold the whipped cream into the cream cheese mixture until combined and fluffy.
Stir in the crushed Oreos, then spread the mixture over the cooled brownie base.
Smooth the top and garnish with extra Oreo pieces or mini Oreos if you like.
Chill in the fridge for at least 4 hours before slicing into bars.