Preheat the oven to 425°F. Line a 12-cup muffin tin with paper liners.
In a large bowl, whisk together the flour, baking powder, baking soda, cinnamon, and salt.
In a medium bowl, whisk together the banana, butter, both sugars, eggs, and vanilla until well incorporated but the bananas are still a bit lumpy. Pour the banana mixture into the flour mixture and stir until combined. Divide the batter among each paper liner (they will be almost full).
Bake for 5 minutes, then reduce the oven temperature to 350°F and continue baking for another 15 minutes or until the centers are springy to the touch and the tops are golden brown. Let the muffins cool in the pan for a few minutes, then remove and place on a wire rack. Serve warm or cool completely on the rack.
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Notes
Don’t overmix the batter. Stop mixing when the dry streaks of flour are just combined. Mixing too much yields dense, tough muffins.
To prevent the cupcake liners from sticking to the muffins, remove the hot muffins from the pan and let them cool on a wire rack. If they cool in the pan, they will steam, and it can cause the paper to stick to the muffin.