01 - Preheat oven to 350°F. Line a 9-inch square baking pan with parchment paper, leaving an overhang on two opposing sides for easy removal.
02 - Set a heatproof bowl over a pot of barely simmering water. Add the chopped chocolate and butter, stirring occasionally until completely melted and smooth. Remove from heat and let cool for 5 minutes.
03 - Whisk the granulated sugar and brown sugar into the melted chocolate mixture until fully combined and no lumps remain.
04 - Add eggs one at a time, whisking thoroughly after each addition. Continue whisking until the batter turns glossy, thick, and slightly aerated.
05 - Sift together the flour, cocoa powder, baking powder, and salt directly into the batter. Gently fold with a spatula until just incorporated—avoid overmixing to keep brownies tender.
06 - Fold in chopped nuts or additional chocolate chips if desired, distributing evenly throughout the batter.
07 - Pour the batter into the prepared baking pan and smooth the surface with an offset spatula, pushing into corners for an even layer.
08 - Bake for 28 to 32 minutes until the center is just set and a toothpick inserted comes out with a few moist crumbs clinging to it. Do not overbake.
09 - Cool brownies completely in the pan set on a wire rack. Once fully cooled, lift the parchment overhang to remove the slab and cut into 12 even squares.