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 over low heat, melt the butter. Once melted, remove from heat and stir in the sugar until well combined.
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 (not wet batter).
Allow the brownies to cool in the pan for at least 15 minutes before cutting into squares.