01 - Preheat oven to 350°F. Line a 9x9-inch baking pan with parchment paper, leaving overhang for easy removal.
02 - Whisk together flour, cocoa powder, baking powder, and salt in a medium bowl until evenly mixed.
03 - In a large bowl, whisk melted butter and sugar until smooth and glossy. Add eggs one at a time, beating thoroughly after each addition. Stir in vanilla extract.
04 - Fold dry ingredients into wet mixture using a spatula until just combined without overmixing.
05 - Gently fold in chocolate chips and three quarters of the chopped walnuts.
06 - Pour batter into prepared pan and smooth surface. Sprinkle remaining quarter cup walnuts evenly over the top.
07 - Bake for 28 to 32 minutes until a toothpick inserted near the center comes out with moist crumbs but no wet batter.
08 - Allow brownies to cool completely in the pan before lifting out via parchment overhang and slicing into 16 squares.