Add the butter to a large pot and cook over low-medium heat until it starts to brown and smells nutty. Do not walk away, it can burn easily.
Once butter is browned place in a heatproof container and chill in the fridge to resolidify. You will need cold, chilled butter for the shortbread.
Chill the Brown Butter
In a large bowl mix together the flour, butter, sugar, and salt. You can use a stand mixer or clean hands and rub together.
Fold in Dry Ingredients
Keep mixing the ingredients until the butter is mixed in and pea-size pieces.
Transfer the dough to pan and press down evenly.
Add to Pan
Once the shortbread is in an even layer use a knife to score the bars. Bake for approximately 20-25 minutes, or until golden brown on the edges.
Score and Bake
Once baked cool on a wire rack for 10 minutes. Sprinkle sugar on top and shake pan side to side to distribute the sugar evenly. Cut on the previously scored marks and let cool completely.