Preheat your oven to 350°F (175°C). Grease a 9x13 inch baking pan or line it with parchment paper for easy removal.
In a medium saucepan, melt the butter over low heat. Once melted, remove from heat and stir in the sugar until well combined. Allow it to cool slightly.
Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
In a separate bowl, whisk together the flour, cocoa powder, salt, and baking powder. Gradually add the dry ingredients to the wet mixture, stirring until just combined. Be careful not to overmix.
If using, fold in the chocolate chips until evenly distributed.
Pour the batter into the prepared baking pan and spread it evenly. Bake for 25-30 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
Allow the brownies to cool in the pan for at least 10 minutes before cutting into squares and serving.