In a mixing bowl, beat together the brown sugar and shortening with an electric mixer until combined.
Add the eggs and vanilla; beat until combined.
Stir together the flour, baking soda, baking powder, and salt. Add dry ingredients and sour cream alternately to beaten mixture. Stir in the 1 cup nuts. Drop by well-rounded teaspoonfuls onto ungreased cookie sheets.
Bake in a 375 degree F oven for 8 to 10 minutes or until tops are lightly browned. Remove to wire rack; cool.
Prepare Brown Butter Frosting. Frost cooled cookies with warm frosting. If you like, sprinkle additional chopped nuts on frosted cookies. Makes 48 cookies.
In a saucepan, melt and cook butter over medium heat until lightly browned. In a mixing bowl, pour the butter over the powdered sugar. Add boiling water and vanilla. Stir until combined. If frosting begins to thicken as it cools, stir in a small amount of hot water. Makes 2/3 cup frosting.