Preheat your oven to 350°F (175°C).
Grease your loaf pan with butter or line it with parchment paper.
In a medium bowl, whisk together the all-purpose flour, baking soda, baking powder, salt, and ground cinnamon (if using). Set aside.
In a large bowl, mash the very ripe bananas until smooth.
Add the melted and cooled butter to the mashed bananas and mix well. Then, stir in the packed brown sugar, slightly beaten eggs, and vanilla extract until combined.
Gently fold the dry ingredients into the wet mixture using a rubber spatula.
If you're using nuts, fold them into the batter at this stage.
Transfer the batter into the prepared loaf pan, smoothing the top with your spatula.
Place the loaf pan in the preheated oven and bake for 60-65 minutes, or until a toothpick inserted into the center comes out clean.
Once baked, let it cool in the pan for about 10 minutes, then transfer to a wire rack to cool completely.
