Preheat your oven to 350°F (175°C).

Lightly grease a muffin tin or line it with a muffin liner.

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

In a separate bowl, mash the banana with a fork until smooth, then mix in the melted butter, sugar, and vanilla extract.

Pour the wet ingredients into the bowl with the dry ingredients and stir gently until just combined.

Scoop the batter into the prepared muffin tin, filling each cup about 2/3 full.

Bake in the preheated oven for 18-20 minutes, until a toothpick inserted comes out clean.

Let the muffin cool in the tin for a few minutes, then transfer to a cooling rack.