Preheat your oven to 350°F (175°C).
In a mixing bowl, melt the butter in the microwave or on the stovetop. Allow it to cool slightly.
Add the granulated sugar to the melted butter and whisk until well combined.
Beat in the eggs and vanilla extract until the mixture is smooth and creamy.
In another bowl, combine the cocoa powder, flour, salt, and baking powder. Whisk them together until well mixed.
Slowly incorporate the dry ingredient mixture into the wet ingredients, stirring until they are just blended together.
Fold in the chocolate chips.
Grease the cast iron skillet with butter or cooking spray. Pour the brownie batter into the skillet, ensuring an even spread.
Place in the preheated oven and bake for approximately 20-25 minutes, or until a toothpick inserted into the center emerges with a few slightly moist crumbs.
Take it out of the oven and allow it to cool for a short while before serving. Top with vanilla ice cream, if desired.