Preheat your oven to 350°F (175°C). Line a 9x13-inch baking pan with parchment paper for easy removal.
In a large mixing bowl, whisk together the melted butter and granulated sugar until smooth and glossy.
Add the eggs one at a time, beating well after each addition to incorporate the eggs fully into the mixture.
Stir in the vanilla extract, then sift the cocoa powder over the wet ingredients, folding gently until the mixture is uniform and shiny.
In a separate bowl, combine the flour, baking powder, and salt. Gradually fold the dry ingredients into the chocolate mixture, just until blended.
Stir in the chocolate chips if using, spreading them evenly through the batter for extra chocolatey pockets.
Pour the batter into the prepared pan and spread evenly with a spatula. Bake for 25 minutes, or until the edges are set but the center remains moist when tested with a toothpick.
Remove from the oven and let the brownies cool completely on a cooling rack. Once cooled, lift out of the pan and cut into 12 squares.
Use edible markers, white chocolate, or icing to draw spooky ghost faces on each brownie. Make large, friendly eyes and wide mouths for a playful look.
Arrange the decorated brownies on a platter and prepare to serve these charming Halloween treats at your party.
