Preheat oven to 350 degrees. Spray a 9×13″ baking dish or line it with parchment paper to easily lift it out of the dish.
Cream butter and sugar until light and fluffy, in a stand mixer or large bowl.
Blend in your eggs, one at a time.
Mix in lemon juice and lemon zest. You may have a curdled look, but this will be fine once you add in the flour.
Stir in salt, baking powder, then fold in your flour, just until incorporated. You do not want to overmix.
Spread into your prepared baking dish and even it out. Bake for 25-30 minutes or until a toothpick in center comes out clean.
Cool 20 minutes. Then remove the brownies, using your parchment paper, or just cool in the pan, on a cooling rack.
Lemon Glaze
While the brownies are cooling, make your glaze.
Whisk powdered sugar to get rid of any clumps, then mix in your lemon juice and a tablespoon of zest. If you want the glaze thicker, add more powdered sugar or for a thinner glaze, add more lemon juice.
Spread over the top of your cooled brownies or spread while still slightly warm for an easier spread. Cut and enjoy!