Step 1: Preheat your oven to 350°F (175°C). Lightly grease a 9x5 inch loaf pan, or line it with parchment paper, leaving a slight overhang on the sides for easy removal.
Step 2: In a large mixing bowl, mash the very ripe bananas thoroughly with a fork until they form a mostly smooth consistency.
Step 3: Stir the melted unsalted butter into the mashed bananas until well incorporated. Then, add the granulated sugar, the beaten large egg, and the pure vanilla extract. Mix everything together until it is fully combined and looks uniform.
Step 4: Sprinkle the baking soda and salt evenly over the wet mixture. Now, gently fold in the all-purpose flour until just combined. Be careful not to overmix; a few small lumps are perfectly fine and contribute to the bread's tender texture.
Step 5: If you are adding optional mix-ins like chopped walnuts or chocolate chips, gently fold them into the batter at this stage.
Step 6: Pour the prepared batter into your greased or lined loaf pan, using a spatula to smooth the top.
Step 7: Bake for 60-65 minutes. Baking times can vary by oven, so keep an eye on it. The banana bread is ready when a wooden toothpick inserted into the center comes out clean or with just a few moist crumbs. A completely clean toothpick might indicate it's slightly overbaked.
Step 8: Once baked, let the banana bread cool in the pan for about 10-15 minutes. This cooling time helps it firm up before you transfer it carefully to a wire rack to cool completely. Slice and serve when cool.