Preheat your oven to 350°F. Line a 9 x 13 inch baking dish with parchment paper.
In a large mixing bowl, combine 1 ¾ cups of all-purpose flour, 1 ¼ cups of granulated sugar, ¼ cup of cornstarch, and ½ teaspoon of salt. Whisk until well mixed.
Whisk in 1 cup of melted butter and 4 large eggs until smooth.
Add 3 tablespoons of lemon zest, 3 tablespoons of lemon juice, 1 teaspoon of lemon extract, and 1 teaspoon of vanilla extract. Stir well until fully incorporated.
Scoop the batter into the prepared pan, smoothing it out evenly.
Bake for approximately 15 minutes. A toothpick inserted should come out mostly clean.
Allow brownies to cool in the pan.
For the glaze, whisk together 2 cups of powdered sugar and 3 tablespoons of lemon juice until smooth.
Lift the brownies out of the pan and cut into squares. Drizzle glaze on top.
