Preheat your oven to 350°F (180°C). Prepare a 9x5-inch loaf pan by greasing it and setting it aside.

Whisk together the flour, baking powder, baking soda, and salt in a medium-sized bowl.

Combine the mashed bananas, sugar, melted butter, eggs, and vanilla extract in a large bowl. Stir the mixture until it is well combined.

Add the dry ingredients to the wet ingredients and stir until they are just combined. Be careful not to overmix the batter.

If using walnuts, gently fold them into the batter.

Pour the batter into the prepared loaf pan and smooth the top.

Bake the banana bread for 55-60 minutes, or until a toothpick inserted into the center comes out clean.

Remove the banana bread from the oven and let it cool in the pan for 10 minutes. Then, transfer it to a wire rack to cool completely.