Preheat your oven to 350°F (175°C). This ensures your brownies bake evenly.
Grease an 8x8-inch baking pan with butter or line it with parchment paper for easy removal.
In your mixing bowl, melt the butter (or heat the oil) if using. Add in the sugar, cocoa, eggs, and vanilla, and mix until smooth.
Stir in the flour and salt (if using). Mix until just combined, being careful not to overmix, as this can lead to denser brownies.
Gently fold in your favorite add-ins, such as chocolate chips or walnuts, for an extra layer of flavor.
Pour the brownie batter into your prepared pan and spread it evenly. Bake in the preheated oven for 20-25 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 transferring them to a wire rack to cool completely. Cut into squares and enjoy!