In a mixing bowl add the dry ingredients: loosely packed flour, baking soda, and cinnamon. Mix well and set aside.
In a separate bowl add the wet ingredients. Add packed brown sugar to softened, room-temperature butter and cream/combine. Then add ripe bananas, eggs, and vanilla extract. Mash/blend until everything is mixed well.
Add the dry ingredients into the wet ingredients.
Mix gently, just enough to combine but do not over-mix (similar to pancake batter).
Butter a 12-cup muffin pan.
Pour batter equally into the 12-cup muffin pan.
Bang the pan on a counter to remove air bubbles and even out the batter.
Bake in the oven for 20 minutes.
Insert a toothpick in the center of a muffin to test. If it comes out clean, then it is done.