Preheat oven to 375 degrees (190 degrees C). Lightly grease 10 muffin cups, or line pan with muffin papers.
In a large bowl, mix together flour, baking soda, baking powder and salt. In another bowl, beat together bananas, sugar, egg and melted butter. Stir the banana mixture into the flour mixture just until moistened. Spoon batter into prepared muffin cups.
In a small bowl, mix together brown sugar, flour and cinnamon. Cut in butter until mixture resembles cornmeal. Sprinkle topping over muffins.
Bake in preheated oven for 18 to 20 minutes, until a toothpick inserted into center of a muffin comes out clean.
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