Preheat your oven to 350°F (175°C) and line a baking pan with parchment paper to prevent sticking.
In a saucepan, melt the unsalted butter over low heat until smooth, then remove from heat and stir in the cocoa powder until well combined and glossy.
In a large mixing bowl, whisk together the granulated sugar and beaten eggs until the mixture is smooth and slightly frothy.
Pour the melted chocolate mixture into the egg mixture, stirring continuously to combine and integrate the flavors.
Sift in the flour, baking powder, and salt over the wet ingredients, then fold everything together gently with a spatula until just combined. The batter will be thick and fudgy.
Stir in most of the chocolate chips into the batter, reserving a few for decoration.
Spread the batter evenly into the prepared pan using a spatula, smoothing the top to ensure even baking.
Bake for about 20-25 minutes, until the edges are set and a toothpick inserted into the center comes out with a few moist crumbs.
Allow the brownies to cool completely in the pan on a cooling rack. This helps them set and makes cutting easier.
While the brownies cool, melt the remaining chocolate chips or melting chocolate in a microwave-safe bowl in 30-second bursts, stirring until smooth.
Use a piping bag or a plastic zip-top bag with the tip cut off to pipe two small eyes on each brownie with melted chocolate, and place a mini marshmallow underneath for the mouth, creating a ghostly face.
Let the decorated brownies sit for a few minutes until the chocolate sets. Then, serve and enjoy these spooky, fudgy Halloween treats!
