Preparation Steps

• Position a rack in the center of the oven and heat to 325°F (165°C). Lightly butter an 8-inch square pan, line it with a parchment sling, and lightly butter the parchment.
• Place the melted butter in a small bowl and stir in the lemon zest. Let it stand 2 minutes to bloom the citrus oils, then cool until just lukewarm.
• In a separate small bowl, whisk together the flour and salt to evenly distribute the salt.
• In a large mixing bowl, vigorously whisk the sugar and eggs for 45–60 seconds until slightly thickened and pale. Whisk in the vanilla and lemon juice until smooth.
• While whisking, slowly stream in the cooled butter–zest mixture until the batter looks glossy and emulsified.
• Add the flour mixture and fold gently with a spatula just until no dry spots remain. Scrape the batter into the prepared pan and smooth the top. Tap the pan once on the counter to release large air bubbles.
• Bake 24–28 minutes, rotating the pan halfway through, until the surface looks matte and a toothpick near the center comes out with a few moist crumbs (not wet batter).
• Cool the pan on a rack for 30–45 minutes, then lift the slab out using the parchment and set on the rack to finish cooling completely before glazing.
• For the glaze, sift the powdered sugar into a bowl. Add the lemon juice and milk and whisk until smooth and thick but pourable, adjusting with a few drops of lemon juice or a spoonful of sugar as needed.
• Spread the glaze over the cooled brownies. Let stand 15 minutes (or chill briefly) until set, then cut into 16 squares and serve.