Use an electric mixer to beat the butter until its light and fluffy.
Add the sugar and continue beating until thoroughly blended.
Blend the salt and flour. Add the flour, about a cup at a time to the butter. Mix until the dough is smooth and soft.
Shape the shortbread:
On a large sheet of parchment, draw a 10x15 rectangle using a pencil and ruler. (I just eye this) Lay the paper on a jelly roll pan or baking sheet: Working quickly, pat or roll the dough into an even layer. Score the dough into 1 x 2 1/2 inch pieces. With a fork, pierce each piece in three places on a diagonal.
Cover the cookies tightly with plastic wrap and refrigerate for at least 2 hours.
Position racks in the upper and lower thirds of the oven and heat to 325
Line two baking sheets with parchment. Cut the chilled dough through the scored lines. Arrange the fingers on the baking sheets with an inch of space between each.
Put the sheets in the oven and reduce heat to 300 Bake for 20 min. Turn the sheets halfway around, switch their positions on the racks, and bake another 14-16 min.
Remove the sheets from the oven.Cool on racks for 5 min. The shortbread will keep for up to a month between layers of waxed paper in an airtight container at room temperature.