Preheat the oven to 350°F (175°C). Grease a 9 × 5-inch loaf pan with butter or cooking spray. Line it with parchment paper if desired, leaving a little overhang on the long sides to make the loaf easier to lift out after baking.
Place the ripe bananas in a large mixing bowl and mash them with a fork until mostly smooth. A few small lumps are fine. Very ripe bananas with brown spots provide the best flavor and moisture.
Add the melted butter and sugar to the mashed bananas and whisk until combined. Beat in the eggs and vanilla extract until the mixture looks smooth and evenly blended.
In a separate bowl, whisk together the all-purpose flour, baking soda, cinnamon, and salt. Mixing the dry ingredients separately helps distribute the baking soda and seasoning throughout the flour.
Add the dry ingredients to the banana mixture. Fold gently with a spatula just until no large streaks of flour remain. Avoid overmixing, which can make the bread dense. Fold in the chopped walnuts or pecans. If the batter seems unusually thick, add the optional milk one tablespoon at a time.
Transfer the batter to the prepared loaf pan and spread it evenly into the corners. Smooth the top with a spatula. For extra texture, sprinkle a few additional chopped nuts over the surface if desired.
Place the pan on the center rack of the preheated oven and bake for 55 to 65 minutes. The top should be golden brown, and a toothpick inserted into the center should come out clean or with a few moist crumbs. If the top browns too quickly, loosely cover it with foil during the final 15 minutes.
Remove the loaf from the oven and let it cool in the pan for 10 to 15 minutes. Carefully lift it out and transfer it to a wire rack to cool further. Allow the bread to cool before slicing so the crumb can set and the slices hold together neatly.