Preheat the oven to 180 degrees. Line and grease a brownie pan and set aside.
Using a spatula, fold in the flour and sugar into the softened butter till you have a dough. Spread evenly on the pan into a thin layer. Bake for 10 minutes.
Meanwhile, prepare the brownie batter. Sift the dry ingredients - flour to salt - into a large bowl.
Whisk together the rest of the ingredients till smooth and sugar is well combined. Fold in the dry ingredients and mix till no streaks of dry ingredients are found.
Take out the shortbread base and spread the brownie on top of it. Bake for 30 minutes till the top is done to touch.
Take out, cool in pan for 10 minutes. Carefully pull out from the pan and cool on a rack completely before slicing and enjoying!