Preheat your oven to 350°F (175°C). Line a 9x13-inch baking pan with parchment paper, leaving some extra overhang for easy removal later. Lightly spray with cooking spray.
In a medium bowl, whisk together the flour and salt. Set aside.
In a large bowl, cream the softened butter and granulated sugar together for 3-4 minutes, until light and fluffy.
Beat in the eggs, one at a time, ensuring each egg is incorporated before adding the next. Stir in the lemon zest, lemon juice, and vanilla extract.
Gently fold the dry mixture into the wet mixture, being careful not to overmix. Stop once no white streaks of flour remain.
Pour the batter evenly into the prepared pan. Bake for 25-30 minutes or until the top is lightly golden, and a toothpick comes out clean from the center. Cool completely on a wire rack.
While brownies cool, whisk together powdered sugar, lemon juice, and lemon zest in a medium bowl. Aim for a pourable consistency—adjust with more lemon juice if needed.
Once the brownies are fully cooled, pour the glaze over the top and spread evenly. Let the glaze set for about 30 minutes before slicing.