All you will need is a wooden spoon to mix everything together- it's just that easy. Preheat your oven to 350 F. Mix the butter into the mashed bananas in a large mixing bowl. Mix in the sugar, egg and vanilla. Then, sprinkle in the baking soda and salt over the mixture and mix it in well. Adding the flour in last, little by little, until fully incorporated. Spray your muffin tin well, to avoid any sticking. Add the batter into each cup until 3/4 way full. Bake for ~15 minutes, checking to see that the center is cooked through. Cool on rack and enjoy!