Preheat the oven to 375 degrees F. Line two 12-cup muffin tins with paper liners or lightly grease with cooking spray.
In a large bowl, whisk together the flour, baking powder, baking soda, cinnamon and salt.
In a medium bowl, whisk together the mashed bananas, brown sugar, melted butter or oil, sour cream, milk and eggs until well-combined.
Add the wet ingredients to the dry ingredients and mix with a rubber spatula until just combined and no dry streaks remain. If adding add-ins like chocolate chips, stir them in when there are still a few dry streaks remaining. Don't over mix or the muffins might be tough and dry in texture.
Scoop the batter into the prepared muffin tin, filling the muffin cups 2/3 full. Bake for 15-17 minutes until a toothpick inserted in the center comes out clean or with a few moist crumbs and the top of the muffins spring back lightly to the touch.
Let cool for 1-2 minutes in the muffin tin before removing to a wire rack to cool completely.
Notes
Half Batch: this recipe can easily be halved to make 10-12 muffins. As a sidenote, the baked and cooled muffins freeze great.Applesauce: I haven't tried replacing the butter/oil with applesauce, but you could experiment.Nutrition Facts: the nutrition facts for this recipe were calculated based on the muffins without the optional add-ins.