Preheat the oven to 350°F and line an 8 x 8-inch baking pan with parchment paper on all sides. Set aside.

In a large microwave-safe bowl, combine the granulated sugar and lemon zest. Rub the zest into the sugar to release the oils. Add the butter and microwave until melted and hot, about 1 minute. Stir with a whisk and microwave for another 15 seconds if needed.

Add the eggs, vanilla extract, and lemon extract. Whisk vigorously until the mixture is glossy and lightened in color, about 30 seconds.

Fold in the flour, salt, and baking powder with a rubber spatula until just combined.

Scrape the batter into the prepared baking pan and spread evenly to the edges.

Bake for 20 to 25 minutes until the edges are set and a butter knife inserted into the middle comes out mostly clean. Set aside to cool.

For the glaze, mix lemon juice, powdered sugar, and vanilla extract in a small bowl. Whisk until smooth, thinning with lemon extract if necessary.

Pour the glaze over the cooled brownies and spread evenly. Allow to set completely before slicing and serving.