Gather the ingredients including unsalted butter, granulated sugar, eggs, vanilla extract, all-purpose flour, cocoa powder, salt, and optional ingredients like chocolate chips or chopped nuts.
Preheat your oven to 350°F (175°C) and line a 8x8 inch baking pan with parchment paper or lightly grease it.
In a microwave-safe bowl, melt the unsalted butter in the microwave in short bursts, stirring between each burst, until fully melted and smooth. Alternatively, melt the butter on the stovetop over low heat.
In a mixing bowl, whisk together the melted butter and granulated sugar until well combined.
Beat in the eggs, one at a time, then stir in the vanilla extract until smooth and creamy.
Sift in the all-purpose flour, cocoa powder, and salt into the wet ingredients. Use a spatula or wooden spoon to gently fold the dry ingredients into the wet ingredients until just combined. Be careful not to overmix.
If desired, fold in chocolate chips, chopped nuts, or any other add-ins of your choice until evenly distributed throughout the batter.
Pour the brownie batter into the prepared baking pan and spread it out evenly with a spatula. Bake in the preheated oven for 20 to 25 minutes, or until a toothpick inserted into the center comes out with moist crumbs. Be careful not to overbake.
Allow the brownies to cool in the pan for at least 10 minutes, then lift them out using the parchment paper and transfer to a wire rack to cool completely. Once cooled, slice into squares and enjoy!