Preheat oven to 375°F, prepare baking sheets with parchment paper or baking spray; set aside.
In a large bowl whisk together flour, baking soda, and salt; set aside.
In a stand mixer fitted with a paddle attachment or a large bowl with hand mixer cream together 1 cup of the granulated sugar (reserve ¼ cup), brown sugar, and vegetable shortening until light and fluffy. Mix in banana, and then the two eggs until combined.
Alternate dry ingredients and buttermilk into the wet mixture and mix on low until fully incorporated.
Fold in 1 cup of chopped walnuts. With two spoons spread out a heaping two spoonful amount of dough onto a prepared cookie sheet. Use the back of the spoon to shape the dough into a circle. Bake about 6 cookies per tray. Sprinkle a little reserved granulated sugar and chopped walnuts on each cookie.