Step 1: Preheat your oven to 350°F (175°C). Grease and flour a 9×5-inch loaf pan, or line with parchment paper, leaving an overhang on the long sides for easy lifting.
Step 2: In a large bowl, mash the very ripe bananas thoroughly with a fork or potato masher until mostly smooth with a few small lumps remaining.
Step 3: In a separate medium bowl, whisk together the all-purpose flour, baking soda, ground cinnamon, and salt. Set aside.
Step 4: In another large bowl, cream together the melted unsalted butter, granulated sugar, and light brown sugar until well combined and smooth.
Step 5: Beat in the eggs one at a time, ensuring each egg is fully incorporated before adding the next. Stir in the mashed bananas and vanilla extract until well combined.
Step 6: Gently fold the dry ingredients into the wet ingredients, mixing just until combined. Be careful not to overmix; a few streaks of flour are acceptable. Then, fold in the sour cream or Greek yogurt until just incorporated. If adding optional mix-ins like chocolate chips or nuts, fold them in now.
Step 7: Pour the batter into your prepared loaf pan, spreading it evenly. You can sprinkle a little extra brown sugar or sliced banana on top for a nice crust.
Step 8: Bake for 55-65 minutes, or until a wooden skewer or toothpick inserted into the center comes out clean. If the top starts to brown too quickly, loosely tent the pan with aluminum foil during the last 15-20 minutes of baking.
Step 9: Once baked, remove the banana bread from the oven and let it cool in the pan on a wire rack for 10-15 minutes. This allows the bread to set and prevents it from sticking.
Step 10: Carefully lift the banana bread out of the pan using the parchment paper overhang (if used) or invert onto the wire rack to cool completely before slicing and serving. Enjoy your homemade classic banana bread recipe!