Preheat the oven to 350°F. Lightly grease a standard (8 1/2x4 1/2x2 1/2–inch) loaf pan or line it with parchment paper.
In a large mixing bowl, mash the bananas with a fork or banana masher.
Add the eggs, sugar, oil, buttermilk, and vanilla. Beat with a hand mixer on medium speed until smoothly combined.
In another bowl, whisk together the flour, baking soda, and salt.
Add the dry ingredients to the banana mixture and mix on low speed just until no dry streaks remain. Do not overmix.
Fold in the nuts, if using, until evenly distributed.
Pour the batter into the prepared loaf pan and smooth the top with a spatula.
Bake for about 1 hour. The bread is done when the top is deep golden, it springs back when lightly pressed, and a toothpick inserted in the center comes out clean or with just a few moist crumbs.
Cool in the pan on a wire rack for 10 minutes.
Run a thin knife around the edges, then carefully remove the bread from the pan and transfer it directly to the rack. Let cool completely before slicing, about 45 minutes.