In a large mixing bowl beat shortening with an electric mixer on medium to high speed for 30 seconds. Add the 1/2 cup brown sugar, baking soda, and salt; beat until combined,scraping sides of bowl occasionally. Beat in egg until combined. Beat in as much of the flour as you can with the mixer. Using a wooden spoon, stir in any remaining flour. Cover and chill dough for 1 to 2 hours or until firm enough to handle.
Meanwhile, combine melted butter, the 2/3 cup brown sugar, walnut flavoring (if desired), and walnuts.
On a lightly floured surface, roll dough into a 12-inch square. Spread walnut mixture evenly over dough; roll up jelly-roll style; seal edges. Wrap in plastic wrap. Chill in the refrigerator at least 3 hours.
Using a sharp knife, cut dough into 1/4-inch-thick slices. Place slices 2 inches apart on an ungreased cookie sheet.
Bake in a 375 degree F oven for 7 to 9 minutes or until edges are lightly browned. Cool on baking sheet for 1 minute. Transfer cookies to a wire rack; cool. Makes about 48 cookies.