01 - Preheat oven to 350°F. Grease a 9x9-inch baking pan and line with parchment paper, ensuring paper overhangs edges for easy removal.
02 - In a medium bowl, whisk together flour, cocoa powder, salt, and baking powder until evenly blended. Set aside.
03 - In a large bowl, combine melted butter and granulated sugar. Whisk vigorously until mixture appears smooth and glossy, approximately 2 minutes.
04 - Beat in eggs one at a time, mixing thoroughly after each addition until fully incorporated. Stir in vanilla extract.
05 - Add dry ingredient mixture to wet mixture. Using a spatula, gently fold until just combined. Stop mixing immediately when flour streaks disappear to prevent tough brownies.
06 - Fold in chocolate chips and chopped walnuts until evenly distributed throughout batter.
07 - Pour batter into prepared pan. Using an offset spatula, spread batter evenly into corners, ensuring smooth surface.
08 - Bake for 28-32 minutes. Test for doneness by inserting toothpick into center; it should emerge with a few moist crumbs but not wet batter.
09 - Cool completely in pan on wire rack, approximately 2 hours. Lift brownies from pan using parchment paper overhang and cut into 16 squares.