01 - Preheat oven to 350°F. Line an 8x8-inch baking pan with parchment paper, leaving enough overhang on two sides to lift the brownies out later.
02 - Set a heatproof bowl over a saucepan of barely simmering water. Add the butter and chopped dark chocolate, stirring gently until completely melted and smooth. Remove from heat and let cool for 5 minutes.
03 - Add the granulated sugar and light brown sugar to the melted chocolate mixture. Whisk until well blended and the mixture looks glossy.
04 - Add the eggs one at a time, whisking thoroughly after each addition until fully incorporated. Stir in the vanilla extract.
05 - Sift the flour, cocoa powder, and salt together directly into the batter. Using a spatula, gently fold the dry ingredients into the wet mixture until just combined. Be careful not to overmix, as this will toughen the texture.
06 - If using, fold the chopped nuts and dark chocolate chips into the batter with a few gentle strokes to distribute evenly.
07 - Pour the batter into the prepared baking pan and spread it into an even layer using a spatula. Smooth the surface for a uniform bake.
08 - Bake for 22 to 25 minutes, or until the top is set and slightly crackly while the center still has a gentle jiggle. Avoid overbaking to maintain a fudgy interior.
09 - Allow the brownies to cool completely in the pan on a wire rack. Once fully set, use the parchment overhang to lift the slab out and cut into 12 squares.