Preheat oven to 350°F (175°C). Line a muffin tin with liners or grease well.
In a bowl, whisk together mashed bananas, melted butter (or oil), sugar, egg, and vanilla.
In another bowl, whisk flour, baking soda, baking powder and salt.
Gradually fold the dry ingredients into the wet mixture. Do not overmix.
Stir in the chocolate chips.
Divide batter evenly into muffin cups, filling about ¾ full.
Bake for 18-22 minutes, or until a toothpick inserted comes out clean.
Let muffins cool for a few minutes in the pan and enjoy!
