Preheat your oven to 350°F.
In a large bowl, whisk together melted butter, sugar, and vanilla until smooth.
Add eggs one at a time, beating well after each addition.
Mix in flour, cocoa powder, and salt until fully combined.
Line a baking pan with parchment or foil, then spray with non-stick spray.
Spread the brownie batter evenly in the prepared pan.
Bake for 25-35 minutes, until the edges are set.
While brownies are baking, melt white chocolate chips in short bursts in the microwave, stirring until smooth. Let the melted chocolate cool to room temperature.
In a bowl, beat cold butter until pale, then add cooled white chocolate, cream cheese, and vanilla. Mix until smooth and creamy.
Once brownies are cooled, fill a piping bag with frosting.
Pipe zigzag lines over the brownies to resemble mummy bandages.
Decorate with candy eyes for a spooky effect.
Cut into rectangles and serve on a Halloween platter or individual plates.