Preheat your oven to 350°F (175°C). Line a muffin tin with paper liners or grease with non-stick cooking spray.

In a large mixing bowl, whisk together the flour, baking powder, baking soda, salt, and sugar until well combined.

In a separate bowl, mix together the melted butter, egg, vanilla extract, buttermilk, and mashed bananas until smooth.

Pour the wet ingredients into the dry ingredients and stir until just combined. Be careful not to overmix; a few lumps are okay.

Divide the batter evenly among the prepared muffin cups, filling each about 3/4 full.

Bake in the preheated oven for 18-20 minutes, or until a toothpick inserted into the center of a muffin comes out clean.

Allow the muffins to cool in the tin for 5 minutes before transferring them to a wire rack to cool completely.

Serve and enjoy! These muffins are best enjoyed fresh but can be stored in an airtight container at room temperature for up to 3 days.