01 - Preheat the oven to 350°F. Line an 8x8-inch baking pan with parchment paper, ensuring the paper overhangs the edges for easy removal.
02 - In a medium bowl, whisk together flour, baking powder, and salt until thoroughly blended. Set aside.
03 - In a large bowl, whisk melted butter and sugar until smooth and glossy. Add eggs one at a time, whisking well after each addition. Stir in lemon juice, lemon zest, and vanilla extract until fully incorporated.
04 - Gently fold the dry ingredients into the wet mixture, mixing just until combined and no dry streaks remain. Take care not to overmix, which can result in dense brownies.
05 - Transfer the batter to the prepared pan. Use a spatula to spread evenly and smooth the top surface.
06 - Bake for 22 to 25 minutes, or until the center is just set and the edges are lightly golden. A toothpick inserted in the center should come out with a few moist crumbs.
07 - Allow the brownies to cool completely in the pan on a wire rack. This step is essential for proper texture and easier glazing.
08 - In a small bowl, whisk powdered sugar and lemon juice until smooth and pourable. If the glaze is too thick, add additional lemon juice 1/2 teaspoon at a time.
09 - Spread the glaze evenly over the cooled brownies. Sprinkle with additional lemon zest if desired. Let the glaze set for 10 to 15 minutes before cutting.
10 - Cut into 16 equal squares using a sharp knife, wiping the blade clean between cuts for neat edges. Serve at room temperature.