Spread 1/4 cup walnuts, chopped on an ungreased sheet pan and bake at 350°F degrees for 6-8 minutes. Cool and store if not using right away.
In a medium sized mixing bowl, sift or whisk the 3 cups all-purpose flour, 1 1/2 teaspoons baking soda and 1/2 teaspoon salt
Using a mixer, cream the 1 cup unsalted butter, and 1 cup granulated sugar until light, about 2 minutes.
Add in 2 large eggs,, one at a time followed by the 1 teaspoon vanilla extract. Mix in the1 cup bananas, mashed, then slowly add the 1/2 cup buttermilk,
Add in the dry ingredients, in 3 separate batches, making sure each addition is fully incorporated before adding the next.
Chill the dough 1 hour. Then, use a medium sized cookie scoop to scoop the cookies onto lined baking sheets. Bake at 375°F 11-13 minutes, or until the centers are completely set when lightly pressed with your fingertip.
Allow cookies to cool on pan 1-2 minutes, then remove to a wire rack to cool completely. Frost when cooled.