Making ghost brownies is a straightforward process. Follow these steps for a successful outcome:

1. Preheat Oven: Preheat your oven to 350°F (175°C). Grease and line a 9×13-inch baking pan with parchment paper for easy removal.
2. Melt Butter: In a saucepan, melt 1 cup of unsalted butter over low heat. Once melted, remove from heat and let cool slightly.
3. Mix Sugar and Eggs: In a large bowl, combine the melted butter and 2 cups of granulated sugar. Stir until smooth. Beat in 4 large eggs, one at a time, followed by 1 teaspoon of vanilla extract. Mix until well combined.
4. Combine Dry Ingredients: In another bowl, sift together 1 cup of all-purpose flour, 1 cup of unsweetened cocoa powder, 1/2 teaspoon salt, and 1/2 teaspoon baking powder.
5. Combine Mixtures: Gradually fold the dry ingredients into the wet ingredients until just blended. Be careful not to overmix.
6. Pour Batter: Pour the brownie batter into the prepared baking pan. Spread it evenly with a spatula.
7. Bake Brownies: Bake in the preheated oven for 25-30 minutes, until a toothpick inserted in the center comes out clean. Let the brownies cool in the pan.
8. Prepare Frosting: While the brownies are cooling, beat together 1 cup of softened unsalted butter, 4 cups of powdered sugar, 1/4 cup of milk, and 1 teaspoon of vanilla extract in a mixing bowl until fluffy and smooth.
9. Frost Brownies: Once the brownies are cool, spread the ghostly frosting over the top with a spatula.
10. Decorate: Using mini chocolate chips or black decorating gel, create eyes and mouths to give your brownies a spooky ghost appearance.

These steps will guide you to create ghost brownies that are as much fun to make as they are to eat.