Preheat your oven to 350°F (175°C) and line the baking pan with parchment paper.
In a large mixing bowl, combine melted butter and granulated sugar, stirring until smooth and fragrant.
Add the eggs one at a time, whisking well after each addition to incorporate air and create a glossy batter.
Stir in the vanilla extract until evenly distributed, then sift in the cocoa powder, flour, baking powder, and salt. Fold gently until the mixture is uniform and slightly thickened.
Pour the batter into the prepared pan, spreading it out evenly with a spatula to create a smooth surface.
Bake for 25 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs. Let the brownies cool completely in the pan on a wire rack.
While the brownies cool, prepare the icing by mixing powdered sugar and milk until smooth and thick enough to spread. Add more milk or powdered sugar as needed for a fudge-like consistency.
Once cooled, cut the brownies into ghost-shaped pieces—using a cookie cutter or freehand shape if desired.
Spread a layer of white icing over each brownie, smoothing the surface for a ghostly appearance.
Place marshmallow ghosts on top of the iced brownies, pressing gently so they sit securely.
Dot each marshmallow ghost with a small edible black candy eye to give it spooky eyes that seem to follow you around.
Arrange the decorated brownies on a serving platter, and enjoy their fudgy texture and playful spooky appearance.
