Mix with your hands the room temperature butter with fine sugar.
Mix the salt & flours together.
Sift in the flours from the air into the butter.
Mix with your hands until blended.
Distribute the dough evenly in a 9" × 12" pan.
Score the dough into the size you want the shortbread to be and poke holes in the dough with a fork.
Cover the dough with plastic wrap & put in the fridge overnight.
The next morning, take the pan out (make sure you have poked enough holes in the dough) & bake in the oven at 325 F for 50 - 60 mins or golden color.
Once you take it out of the oven, cut the shortbread into the sizes you want. (don't wait too long or it will be difficult to cut).