Preheat oven to 375°F (190°C)
Line or grease 10 muffin cups.
In a medium bowl, whisk together flour, baking soda, baking powder, and salt
In a separate bowl, combine mashed bananas, sugar, egg, and melted butter.
Add the wet ingredients to the dry ingredients and stir just until combined.
Do not overmix.Divide batter evenly among prepared muffin cups
For Crumb Topping: In a small bowl, combine brown sugar, flour, cinnamon, and butter until crumbly.
Sprinkle crumb topping evenly over each muffin.
Bake for 18–20 minutes, or until a toothpick inserted in the center comes out clean
Cool in the pan for 5 minutes before transferring to a wire rack.