Preheat the oven to 350°F. Spray a 9x5-inch loaf pan with nonstick cooking spray.

Place the bananas in a large mixing bowl and mash until mostly smooth.

Add the melted butter, brown sugar, egg, and vanilla extract. Stir until well combined.

In a separate bowl, whisk together the flour, baking powder, baking soda, salt, and cinnamon.

Gradually add the dry ingredients to the banana mixture and stir just until combined. Do not overmix.

Pour the batter into the prepared loaf pan and spread it evenly.

Bake for 50–55 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs. If the top begins to brown too quickly, loosely tent the loaf with aluminum foil.

Let the bread cool in the pan for 10–15 minutes.

Carefully remove the bread from the pan and transfer it to a wire rack to cool completely.

Slice into 10 servings and serve.