Preheat oven to 375 degrees F.
Coat muffin pans with non-stick cooking spray, or use paper liners.
Combine together the flour, baking powder, baking soda, and salt; stir with whisk and set aside.
Combine bananas, egg, vanilla, peanut butter, sugar and melted butter in a large bowl. F
old in flour mixture, and mix until smooth. DO NOT OVER MIX.
**If using white whole wheat flour, cover and let rest in fridge for 30 minutes. Skip this step if using all-purpose flour.
Scoop into muffin pans.
Bake muffins for 18-20 minutes or until a toothpick stuck in the muffins comes out clean. Let cool for a few minutes minutes before turning the muffins out of pan.
Serve warm or at room temperature.