Preheat your oven to 175°C (350°F) and line your baking pan with parchment paper or give it a light spray of non-stick spray.
Melt the butter gently in a small saucepan over low heat or microwave it in short bursts until just shimmering. Let it cool slightly while you prepare the other ingredients.
In a large bowl, whisk together the sugar, eggs, and vanilla extract until the mixture is smooth, slightly frothy, and the sugar begins to dissolve, about 2 minutes.
Pour the cooled melted butter into the egg mixture and stir until fully combined, creating a rich, glossy base.
Sift together the cocoa powder, flour, and a pinch of salt if using, then gently fold the dry ingredients into the wet mixture with a spatula until just combined. Do not overmix to keep the bars tender.
Stir in the chopped dark chocolate or chocolate chips, and any optional mix-ins like nuts or candies, folding until evenly distributed.
Pour the batter into your prepared pan and spread it out evenly with a spatula. Tap the pan gently on the counter to settle the batter and remove air bubbles.
Bake for 22-25 minutes, until the edges are set and slightly pull away from the pan, but the center remains fudgy and moist. The top will crack and look matte.
Remove from the oven and let the bars cool in the pan on a wire rack for at least 15 minutes. Cooling helps them set, making slicing easier and cleaner.
Once cooled, lift the bars out of the pan using the parchment paper and slice into squares or rectangles with a sharp knife. Serve at room temperature for that perfect fudgy texture.
Enjoy your messy, chocolatey brownie bars—perfect for sharing or savoring all on your own!
