Preheat the oven to 350°F and line a standard 12 cup muffin pan with paper liners. Set aside. (Alternatively, spray the wells liberally with cooking spray.)
In a medium bowl whisk together flour, baking powder, baking soda, and salt.
In a large separate bowl combine sugar, eggs, oil, vanilla extract, and mashed banana until well combined. Note: The batter will be lumpy from the bananas.
Add the flour mixture to the wet ingredients and stir to combine flour until it's fully moistened. Stir in 2/3 cup chocolate chips, reserving a 1/3 cup for the tops.
Use an ice cream scoop or a measuring cup to evenly divide the batter between the muffin cups, filling them about 2/3 full. Sprinkle tops with reserved chocolate chips. (Depending on how the batter is divided, you may yield more. Have an extra pan handy.)
Bake the muffins for 20- 22 minutes or until a toothpick comes out clean when inserted into the centers.
Cool in the pan for 5 minutes, then remove to a cooling rack to cool completely.
Store in an airtight container chilled or at room temperature for up to 2 days.
Notes
Sugar - You can use dark brown sugar or light brown sugar in this muffin recipe. The darker the sugar, the more of a molasses flavor it will have. The kind of sugar won't change the amount.
Chocolate Chips - Instead of topping the muffins with more chocolate chips, you can tuck a round slice of banana or some chopped banana to the top of each muffin as a last step before baking.
Nuts - You can stir in 1/2 cup of chopped pecans or walnuts to the batter.
Oil - You can use 1/2 cup of salted butter, melted in place of oil.
Chocolate Chip Substitution - You can replace the chocolate chips with peanut butter chips or butterscotch chips for a flavor twist.
Bake Without Paper Liners - You can also bake banana muffins without muffin liners. Give the wells of the muffin pan a good spray with cooking spray and drop the batter directly into the pan.
Mash the Bananas - I like having some chunks of banana in the muffins so I don’t completely mash them into a puree-like consistency. It's fine to keep some small banana chunks.
Use a Scoop for Even Portions - When dividing the batter I almost always use an ice cream scoop. It keeps the batter more concise for even batter distribution into the cups of the muffin pan important for even baking