Preheat oven to 350°F. Line a 9x9 square glass baking dish with parchment paper and set it aside.
Mix together oil and sugar in a large mixing bowl. Use a hand mixer or standing mixer to combine.
Beat in lemon extract, vanilla extract, lemon zest, and lemon juice. Add one egg at a time and then the egg yolk, mixing well between each one.
Stir together the flour, salt, and baking powder and add to the wet mixture.
Beat together 1 to 2 minutes until fluffy and well combined.
Spread batter into prepared baking dish. Bake for 25 minutes. Remove from the oven and allow to cool for 30 minutes before preparing glaze.
Whisk together the powdered sugar, water, lemon extract, and lemon juice until a smooth paste-like glaze forms.
Spread glaze over the brownies. Allow brownies to cool completely and the glaze will set so that it’s dry to the touch. Cut into pieces and serve.