Preheat the oven to 350°F (175°C) and grease a 9x13 inch baking pan.
Melt the butter in a saucepan over medium heat, then remove from the heat and stir in both sugars until combined.
Allow the mixture to cool slightly, then add in the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
Sift together the flour, cocoa powder, and salt in a separate bowl before gradually folding it into the wet mixture.
Stir in the chocolate chips and nuts (if using) until evenly distributed throughout the batter.
Pour the brownie batter into the prepared baking pan, smoothing it out into an even layer.
Bake in the preheated oven for 20-25 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.
Allow the brownies to cool in the pan for about 10 minutes before transferring them to a wire rack to cool completely.
Once cooled, cut into squares and serve with your favorite toppings, if desired.