Preheat the oven to 350°F. Line a 12-cup muffin tin with paper liners or grease each muffin cup well. In a large mixing bowl, mash the very ripe bananas until mostly smooth. A few small banana pieces are fine and will give the muffins good texture.
Add the melted butter, brown sugar, eggs, vanilla extract, and milk to the mashed bananas. Stir until the wet ingredients are well combined.
In a separate bowl, whisk together the soft milled wheat flour, baking soda, baking powder, salt, and cinnamon if using.
Add the dry ingredients to the banana mixture and stir gently until just combined. Do not overmix the batter, or the muffins can turn out dense.
Fold in the chocolate chips.
Spoon the batter evenly into the prepared muffin tin, filling each cup about ¾ full. Sprinkle a few extra chocolate chips on top if desired.
Bake for 18 to 24 minutes, or until the tops are set and a toothpick inserted into the center of a muffin comes out clean or with a few moist crumbs. Let the muffins cool in the pan for about 5 minutes, then move them to a cooling rack.