Preheat your oven to 350°F (175°C). Grease and flour a 9x5-inch (23x13 cm) loaf pan, or line with parchment paper leaving an overhang on the long sides for easy removal.

In a large mixing bowl, mash the very ripe bananas with a fork until mostly smooth but with a few small lumps remaining. Set aside.

In a separate medium bowl, whisk together the all-purpose flour, granulated sugar, baking soda, salt, and ground cinnamon (if using). Make sure there are no lumps and the ingredients are well combined.

To the mashed bananas, add the room temperature eggs, melted and cooled unsalted butter, vanilla extract, and sour cream (or yogurt). Whisk until just combined. Do not overmix this mixture.

Pour the wet ingredient mixture into the dry ingredient mixture. Using a spatula or wooden spoon, gently fold until just combined. Be careful not to overmix; a few streaks of flour are fine. Overmixing will result in a tough banana bread.

If using, gently fold in the chocolate chips and/or chopped nuts into the batter.

Pour the batter evenly into the prepared loaf pan.

Bake for 55-65 minutes, or until a wooden skewer or toothpick inserted into the center comes out clean or with only moist crumbs attached (no wet batter). If the top starts to brown too quickly, you can loosely tent it with aluminum foil after about 40 minutes.

Once baked, remove the loaf pan 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 makes it easier to remove.

After cooling in the pan, carefully lift the banana bread out of the pan using the parchment paper overhang (or invert it onto the rack). Let it cool completely on the wire rack before slicing and serving. This ensures the bread is fully set and moist.