Preheat your oven to 350°F (175°C).
Grease and line a 9x13-inch baking pan with parchment paper.
Melt the butter in a large saucepan over low heat, then remove from heat.
Stir in granulated sugar, followed by eggs one at a time, and then the vanilla extract.
Sift in the cocoa powder, flour, baking powder, and salt. Mix until combined.
Fold in chocolate chips if desired.
Pour the batter into the prepared pan and smooth the top.
Bake for 20-25 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.
Remove from the oven and let cool in the pan for about 15 minutes.
Transfer to a wire rack to cool completely before cutting into squares.