1. Preheat oven to 350*
2. Line to cookies with parchment paper
3. Whisk flour, salt, baking powder, and baking soda together in a medium bowl; stir in nuts and crystallized ginger
4. In a large bowl with an electric mixer on medium high speed, beat butter until creamy, about 2 minutes.
5. Add brown sugar gradually, beating until light and fluffy, about 3 minutes.
6. Beat in spices.
7. Add eggs one at a time, beating well after each.
8. Beat in pumpkin puree
9. Mixture might look curdled;that's okay.
10. Add about one-third of flour mixture and mix on low speed.
11. Gradually add remaining flour, mixing just until blended.
12. Drop by generously rounded tablespoon 2 inches apart on cookie sheets.
13. Bake until light golden brown and just dry to touch, but still a little soft inside, about 15 minutes. You should beable to gently lift edge of a cookie up from sheet with spatula, and a toothpick will test clean.
14. Slide parchment onto racks to cool cookies completely.
15. To make frosting, combine butter and brown sugar in a small saucepan over medium heat, stirring occasionally, until butter melts.
16. Bring to a boil and let boil 1 minute.
17. Scrape mixture into a medium bowl and allow to cool 5 minutes.
18. Add heavy cream and whip with mixer until combined.
19. Add confectioners sugar and beat until thick, creamy and spreadable.
20. Right before serving, spread frosting on each cookie using a small offset spatula.