Preheat oven to 350ºF and line a standard 12 cup muffin pan with paper liners.
In a large mixing bowl, stir together the butter and sugar until combined.
Add the egg, vanilla extract, milk, and mashed bananas and mix well.
Add the flour, baking powder, baking soda, and salt to the bowl and stir just until no streaks of flour remain.
Fold in the chocolate chips.
Using a 4 TBS cookie scoop, scoop the batter evenly into the 12 muffin cups. This recipe makes an even 12 muffins, so you should have just enough batter to fill them all.
Bake muffins for 24-26 minutes or until the tops are lightly golden brown and a toothpick inserted into the center comes out clean or with a few moist crumbs attached.
Allow the muffins to cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.
Store muffins in an airtight container for 3-4 days or freeze for up to 3 months.
Notes
Use very ripe bananas. The browner (or even black) the bananas are, the sweeter and more flavorful your muffins will be.
Measure the bananas. Two bananas can vary quite a bit in size, so measuring 1 cup of mashed banana will give you the most consistent results.
Don’t overmix the batter. Make sure to stir just until the flour disappears. Overmixing can make muffins dense instead of soft and tender.
Check for doneness around the 20 minute mark, since all ovens are a little different. The muffins are ready when the tops spring back lightly when touched and a toothpick inserted into the center comes out clean or with a few moist crumbs.
You can use your favorite chips. Milk chocolate, dark chocolate, or mini chocolate chips all work well.