01 - Preheat oven to 350°F. Line a 9-inch square baking pan with parchment paper, leaving an overhang on two opposite sides for easy removal.
02 - In a heatproof bowl set over a pot of simmering water, melt the chocolate and butter together, stirring until completely smooth. Remove from heat and let cool slightly for about 5 minutes.
03 - Whisk the granulated sugar and brown sugar into the melted chocolate mixture until fully combined and no sugar granules remain visible.
04 - Add eggs one at a time, whisking thoroughly after each addition. Continue mixing until the batter becomes glossy, thick, and well emulsified.
05 - Sift together the flour, cocoa powder, baking powder, and salt directly into the chocolate batter. Fold gently with a spatula until just incorporated—do not overmix to keep brownies tender.
06 - Gently fold in chopped nuts or additional chocolate chips if desired, distributing evenly throughout the batter.
07 - Pour the batter into the prepared pan and spread evenly. Smooth the surface with a spatula for uniform baking.
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. Avoid overbaking for the fudgiest texture.
09 - Allow brownies to cool completely in the pan on a wire rack. Use the parchment overhang to lift the slab out, then cut into 12 even squares.