Step 1: Preheat your oven to 350°F (175°C). Grease and flour a 9x5-inch loaf pan, or line with parchment paper, leaving an overhang on the long sides.
Step 2: In a medium bowl, whisk together the all-purpose flour, baking soda, ground cinnamon, and salt. Set aside.
Step 3: In a large bowl, mash the very ripe bananas with a fork or potato masher until mostly smooth with a few small lumps remaining. Aim for about 1.5 cups of mashed banana.
Step 4: Add the melted butter, granulated sugar, brown sugar, eggs, and vanilla extract to the mashed bananas. Whisk until well combined and smooth.
Step 5: Gradually add the dry ingredients to the wet ingredients, mixing with a spoon or spatula until just combined. Be careful not to overmix; a few streaks of flour are acceptable.
Step 6: If adding optional mix-ins like chocolate chips or nuts, gently fold them into the batter until evenly distributed.
Step 7: Pour the batter into the prepared loaf pan and spread evenly. Bake for 55-70 minutes, or until a wooden skewer or toothpick inserted into the center comes out clean. If the top browns too quickly, loosely tent with foil.
Step 8: Remove the loaf from the oven and let it cool in the pan for 10-15 minutes. Then, carefully lift it out onto a wire rack to cool completely before slicing and serving.