Preheat your oven to 350°F (175°C) to ensure even baking.
Grease your loaf pan with butter or non-stick spray.
In a large bowl, whisk together the flour, baking soda, baking powder, salt, and cinnamon (if using).
In another bowl, mash the bananas until smooth.
Add the melted butter to the bananas and mix well. Stir in the brown sugar, beaten eggs, and vanilla extract.
Pour the banana mixture into the dry ingredients and fold gently until just combined.
If using, fold in the walnuts or pecans.
Pour the batter into the prepared loaf pan and bake for 55-65 minutes, or until a toothpick comes out clean.
Let the banana bread cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before slicing.
