Preheat oven to 375°F (190°C). Grease a 12-cup muffin tin or line with muffin liners.
In a large bowl, mix together 1.5 cups flour, baking powder, baking soda, 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, 2 tablespoons flour, and cinnamon. Cut in 1 tablespoon butter until mixture resembles coarse cornmeal. Sprinkle topping over muffins.
Bake in preheated oven for 18 to 20 minutes, until a toothpick inserted into the center of a muffin comes out clean.