To begin, preheat your oven to 350. Spray a muffin pan with non-stick spray.
To a large mixing bowl, add your butter and brown sugar and beat them together with a mixer till creamy. Add your banana and vanilla and beat again till mostly smooth. Add your milk and eggs and blend till combined.
To the same bowl, add your flour, baking powder, baking soda, salt, cinnamon and mix together till you have a thick muffin batter. Add your chocolate chips and fold them in.
Fill each muffin cavity about 3/4 way full.
Bake in the oven for 18-21 minutes, or till a toothpick inserted comes out clean and the top is springy to touch.
Let cool, then devour!
Stored in an airtight container, these last on the counter for 1-3 days and in the fridge for about a week.