Preheat oven to 350°F (175°C) and center rack. Coat a 9×5-inch loaf pan with cooking spray and parchment paper for easy removal.
Cream butter and sugar with a mixer until pale and fluffy (3-4 minutes).
Add mashed bananas and mix thoroughly with a potato masher or fork. For chunky texture, gently fold ripened banana pieces.
Beat in eggs, then stir in milk, vanilla, and salt. Scrape bowl well to blend.
Gradually add flour and baking soda, mixing until just combined. Overmixing creates a denser loaf. Stir gently with a spatula for a lighter texture.
Fold in chopped walnuts for crunch.
Pour batter into prepared pan and smooth top. Bake for 50-60 minutes, until a toothpick inserted comes out clean. If top browns too quickly, cover loosely with foil.
Cool in pan for 10 minutes, then transfer to a wire rack. Slice and serve.