Preheat oven to 350°. In a large bowl, stir together flour, sugar, baking soda and salt. In another bowl, combine the eggs, bananas, oil, buttermilk and vanilla; add to flour mixture, stirring just until combined. Fold in nuts. , Pour into a greased or parchment-lined 9x5-in. loaf pan. If desired, sprinkle with additional walnuts. Bake until a toothpick comes out clean, 1-1/4 to 1-1/2 hours. Cool in pan for 15 minutes before removing to a wire rack.