Preheat your oven to 180°C (350°F). Grease and line a 20cm x 20cm (8x8 inches) square baking pan with parchment paper, leaving an overhang on two opposite sides for easy removal.
Break the dark chocolate into small pieces and chop the unsalted butter into chunks. Place them in a heatproof bowl and melt them together. You can do this by either microwaving in 20-second intervals, stirring between each, or by using a double boiler on the stovetop. Once melted, let it cool for a few minutes.
In a separate mixing bowl, whisk the eggs, granulated sugar, and vanilla extract until well combined.
Pour the melted chocolate and butter mixture into the egg and sugar mixture, and whisk until smooth and glossy.
Sift in the all-purpose flour, cocoa powder, and salt. Gently fold the dry ingredients into the wet ingredients until just combined. Be careful not to overmix; you want the batter to be just combined.
If you're adding chopped nuts, fold them into the batter.
Pour the brownie batter into the prepared baking pan and spread it evenly.
Bake in the preheated oven for approximately 25 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs attached. The exact baking time may vary depending on your oven, so keep an eye on them to avoid overbaking.
Once done, remove the brownies from the oven and let them cool completely in the pan on a wire rack. This helps them set properly and develop a fudgy texture.
Once the brownies are completely cool, use the parchment paper overhangs to lift them out of the pan. Place them on a cutting board and cut into squares or rectangles as desired.Enjoy your homemade chocolate brownies! You can dust them with powdered sugar or serve them with a scoop of vanilla ice cream for an extra treat.