Preheat Oven to 375 degrees. Grease 10 muffin tins or line with muffin cups.
In a large bowl, whisk together the flour, salt, baking soda, and baking powder. Set aside.
In another bowl, mix together the bananas, egg, white sugar, and butter.
Add the banana puree to the dry ingredients, mixing well.
Using a 1/3 measuring cup, pour the batter into the 10 muffin tins.
For the crumble toping, in a small bowl, combine the brown sugar, flour, cinnamon, and butter. Using a fork, whish until a crumbled mixture. Spoon by the tablespoon full on top of the muffins, liberally.