I have made this recipe for Christmas for many, many years. I have one son and several grandchildren who would not think it was Christmas if they didn't have these cookies. I cannot remember where I got the original recipe but I probably make at least 4 times this amount during the Holiday season.
Whisk together flour and salt. Cut in butter or margarine. Add brown sugar and mix well. Press dough evenly into bottom of greased and floured (or sprayed) 9x13 1/2" pan with floured spoon. Bake 15 minutes and cool slightly.
In top of double boiler or in microwave melt butterscotch pieces, corn syrup, shortening, water and salt. Stir in 2 cups coarsely chopped nuts. Spoon evenly over slightly cooled cookie layer. Bake 8 more minutes. Cool and cut into squares.
HINT: If you cannot get the butterscotch-nut layer to spread evenly - place in oven for several minutes and then tilt pan and spread to corners with spoon.