Preheat oven to 350°F. Grease and flour 2 8-inch cake pans.
In a large bowl, sift together flour, baking soda, baking powder and salt.
In a mixing bowl, cream together butter and sugar. Add in egg yolks, one at a time.
In a third bowl, combine mashed banana and buttermilk.
Slowly incorporate flour mixture and banana mixture, alternating between the two and ending on the flour.
In a fourth bowl (so many bowls!), beat egg whites until they are stiff. Fold into the batter.
Divide the batter into the two pans and bake for 30-35 minutes or until a toothpick comes out clean.
Let cool in pans for 5 minutes, then remove to a cooling rack.
Meanwhile, beat the first four filling ingredients until blended. Fold in the walnuts, set aside.
Beat butter with a mixer for 5-6 minutes. Add in vanilla, buttermilk and banana. Beat for another minute or two. Slowly incorporate powdered sugar until desired consistency.
When cake is cool, level off one layer. Spread filling over the layer and top with the other cake. Frost and decorate.
Recipe by HoboTrashcan at https://www.hobotrashcan.com/2016/03/10/bacon-and-legs-cowboys-4-angel-food-cake-gigolos-inspired-recipe/