Preheat oven to 425 degrees. Lightly spray a 12 cup standard muffin tin.
In a large mixing bowl place 3 very ripe peeled bananas. Mash them with a fork until smooth. Mix in brown sugar & melted butter. Whisk in eggs, sour cream & vanilla until a smooth batter comes together.
In a medium bowl whisk together flour, baking soda, baking powder, cinnamon, and salt until evenly distributed.
Add the dry ingredients into the wet ingredients and fold together using a spatula. Don't over mix.
Using a 1/4 cup measuring cup or a large cookie scoop, divide batter between the 12 prepared muffin tin cups.
Bake muffins in preheated oven for 5 minutes. Without open door of oven, lower oven temperature to 350 degrees and bake an additional 15-18 minutes until the muffins are golden brown. Test with a toothpick inserted in center of muffin. Toothpick should come out clean. If batter is on toothpick bake an additional 2-3 minutes.
Allow muffins to cool in muffin pan for 5 minutes. Remove muffins to a wire cooling rack to cool and additional 5 minutes before serving.