Preheat your oven to 350°F (175°C). Melt the unsalted butter in a medium saucepan over low heat. Whisk in the granulated sugar, followed by the eggs one at a time, and then blend in the vanilla extract until smooth.

In a separate bowl, whisk together the flour, cocoa powder, baking powder, and salt. Gradually combine this dry mixture into the wet batter, stirring gently until incorporated.

Pour the batter into a greased 9x13-inch pan and bake for 25-30 minutes or until a toothpick comes out with moist crumbs. Let the brownies cool completely.

Melt chocolate chips in 30-second intervals in a microwave-safe bowl. Dip the top of each ice cream cone into the melted chocolate, then sprinkle with Halloween-themed sprinkles and let them dry.

In a mixing bowl, combine powdered sugar, milk, vanilla extract, and green food coloring, mixing until smooth. Spread this frosting over the cooled brownies.

Place the upside-down chocolate ice cream cone on each brownie, pressing gently to secure it. Decorate with additional sprinkles.