Cream shortening, white sugar and pumpkin. Add eggs and mix well. Sift together the baking soda, ground cinnamon, salt and flour. Add to pumpkin mixture and mix well. Drop from spoon to cookie sheet. Bake 10 minutes at 350 degrees F (175 degrees C). To Make Frosting: Cook butter, milk, and brown sugar until dissolved. Cool and add confectioners' sugar and vanilla. Spread over warm cookies.