Preheat the oven to 350°F (175°C).

Grease a 9x9 inch baking pan or line it with parchment paper.

In a mixing bowl, combine the melted butter and granulated sugar, stirring until fully incorporated and smooth.

Add the eggs and vanilla extract and whisk until the mixture is smooth and creamy.

In a separate bowl, whisk together the cocoa powder, all-purpose flour, salt, and baking powder.

Gradually add the dry ingredients to the wet ingredients, stirring just until combined to avoid overmixing.

Pour the batter into the prepared baking pan and use a spatula to spread it evenly.

Bake in the preheated oven for 25 to 30 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.

Let the brownies cool completely in the pan before cutting into squares for clean edges.