01 - Preheat oven to 350°F. Line an 8x8-inch baking pan with parchment paper, ensuring coverage extends over edges for easy removal.
02 - In a medium bowl, whisk together all-purpose flour, baking powder, and salt until thoroughly blended. Set aside.
03 - In a large bowl, whisk melted butter and granulated sugar until smooth and glossy. Add eggs one at a time, whisking thoroughly after each addition until fully incorporated.
04 - Stir in fresh lemon juice, lemon zest, and vanilla extract until evenly distributed throughout the mixture.
05 - Gently fold dry ingredients into wet mixture, mixing just until combined and no dry streaks remain. Avoid overmixing to maintain tender texture.
06 - Pour batter into prepared pan, smoothing top with spatula. Bake for 22 to 25 minutes until center is just set and edges are lightly golden.
07 - Allow brownies to cool completely in pan on wire rack before glazing or cutting to ensure clean slices.
08 - In small bowl, whisk powdered sugar and lemon juice until smooth and pourable. Spread evenly over cooled brownies and sprinkle with additional lemon zest.
09 - Cut into 16 equal squares using sharp knife, wiping blade between cuts for clean edges.