Preheat your oven to 350F and line a baking sheet with parchment paper.
In a mixing bowl, combine the flour, baking powder, baking soda, and salt.
In a separate bowl, beat the butter, brown sugar, egg, and vanilla extract together until well combined.
Add the mashed bananas to the butter mixture and mix well.
Add the wet ingredients to the dry ingredients and mix until a dough forms.
Use a cookie scoop or spoon to form the dough into 12 balls and place on the prepared baking sheet.
Flatten the cookies slightly with the back of a fork.
Bake for 15-18 minutes, or until the edges are golden brown.
Remove from the oven and let cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.