Melt the butter in a medium saucepan over low heat, stirring occasionally. Remove from heat and let cool.

In a large mixing bowl, combine melted butter and granulated sugar. Mix until smooth and glossy.

Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.

Whisk together flour, cocoa powder, salt, and baking powder in a separate bowl. Gradually add to the wet ingredients.

Pour the batter into a prepared 9×13 inch baking pan and spread evenly.

Bake in a preheated oven at 350°F (175°C) for 25-30 minutes. Check with a toothpick for doneness.

Cool brownies completely in the pan on a wire rack.

While cooling, optionally melt chocolate and dip tops of ice cream cones. Roll in sprinkles.

Mix powdered sugar, milk, vanilla extract, and green food coloring until smooth to make frosting.

Frost the cooled brownies with the green frosting.

Place an upside-down chocolate cone on each brownie to resemble a witch's hat.