Preheat your oven to 350°F (175°C) and line a baking pan with parchment paper to prevent sticking.
In a large mixing bowl, whisk together the melted butter and sugar until smooth and glossy, releasing a rich chocolate aroma.
Add the eggs one at a time, whisking well after each addition, until the batter is thick and velvety.
Stir in the vanilla extract, then sift the cocoa powder, flour, baking powder, and salt into the mixture, folding gently until just combined and the batter is smooth.
Pour the batter into the prepared baking pan and spread evenly with a spatula, smoothing the top for an even bake.
Bake for about 25-30 minutes, or until a toothpick inserted into the center comes out with moist crumbs. Let the brownies cool completely in the pan.
Once cooled, lift the brownies out of the pan using the parchment paper and place on a flat surface. Cut into individual squares or desired shapes.
Melt the white chocolate melts in a microwave in short bursts, stirring until smooth. Use a piping bag or a spoon to add two small drops of melted white chocolate onto each brownie to create the ghost eyes.
Place a mini marshmallow on top of each white chocolate dot to complete the ghost faces, and gently press to secure.
If desired, sprinkle a little edible shimmer powder or glitter on the ghosts to give them an eerie, glowing appearance.
Arrange the ghost brownies on a serving plate, and enjoy these soft, fudgy treats with their playful and spooky decor!
