Zest the lemon peel of one lemon. Squeeze out the lemon juice as well.
Preheat the oven to 350°F. Line a 9"x9" baking dish with parchment paper.
Add the softened butter, brown sugar and lemon zest to a large bowl. Use an electric mixer to cream everything together.
Add in the eggs and yolk one at a time, mixing thoroughly before adding another.
Add in the vanilla extract and lemon extract and mix.
In a medium bowl, mix together the flour and baking powder.
Add half of the flour to the wet mixture and mix in.
Add the other half and mix in.
Pour the batter into the greased baking dish. Bake for 22-25 minutes. Let cool for 30 minutes before removing from pan. Transfer to a rack to cool completely.
Add the lemon glaze ingredients together in a small bowl. Mix everything together.
Spread overtop of the brownies with a spatula. Slice into squares, serve and enjoy.