Preheat the oven to 350°F (175°C) and grease a baking pan.

In a mixing bowl, combine the dry ingredients: flour, baking powder, baking soda, and salt.

In another bowl, mix the mashed bananas, granulated sugar, brown sugar, melted butter, egg, and vanilla extract until well combined.

Gradually add the dry ingredients to the wet ingredients, stirring until just combined.

Pour the batter into the prepared baking pan and spread evenly.

Bake in the preheated oven for 25-30 minutes or until a toothpick inserted in the center comes out clean.

Allow to cool before cutting into bars.