Preheat your oven to 350°F (175°C).
Grease a 9x13-inch baking pan.
Melt the butter in a large saucepan over medium heat.
Stir in the sugar until well combined.
Remove from heat and let it cool slightly.
Beat in the eggs, one at a time, mixing well after each addition.
Add the vanilla extract and mix.
In a separate bowl, whisk together the flour, cocoa powder, baking powder, and salt.
Gradually add the dry ingredients to the wet mixture, stirring until just combined.
Pour the batter into the prepared pan and spread evenly.
Bake for 30 minutes, or until a toothpick comes out with a few moist crumbs.
Let the brownies cool completely before frosting.