Preheat oven to 350 degree.
Coat muffin pans with non-stick spray, or use paper liners.
Sift together the flour, baking powder, baking soda, and salt, set aside.
Combine bananas, sugar, egg, vanilla, and melted butter in a large bowl.
Fold in flour mixture, blueberries, and mix until dry ingredients are just combined. Do not over-mix.
Fill the muffin cups till the ¾th mark.
Bake in preheated oven for 15-20 minutes.
These stay well up to 3 days if stored in an airtight container.