Preheat your oven to 350°F (175°C).
Grease a 9x13 inch baking pan.
Melt the butter in a large saucepan over medium heat.
Remove from heat and stir in sugar, eggs, and vanilla extract.
Add the cocoa powder, flour, baking powder, and salt to the mixture.
Fold in the chocolate chips and nuts (if using).
Pour the batter into the prepared baking pan and smooth the top.
Bake the brownies for 25-30 minutes, until a toothpick comes out with a few moist crumbs.
Let the brownies cool in the pan on a wire rack before cutting them into squares. Enjoy!