Preheat oven to 375F. Grease cookie sheet; set aside.
In a large mixing bowl, beat the brown sugar and shortening with electric mixer on medium speed until well mixed. Add baking soda, baking powder, and salt. Beat until combined. Beat in eggs and vanilla, until well mixed. Add the flour and sour cream, alternating the two, mixing well after each addition. Stir in 2/3 cup chopped walnuts.
Drop dough by rounded teaspoons 2 inches apart on cookie sheets. Bake for 10-12 minutes, or until edges are lightly browned. Cool completely.
In a medium saucepan, heat and stir 1/2 cup butter until golden brown, do not scorch! Remove from heat. Stir in powdered sugar, water and vanilla. Using a wooden spoon, mix until icing can spread easy. You can add additional water, if needed to make icing spread. Spread on each cookie. Makes 5 dozen cookies.