For the crumb topping, stir the flour, sugar, and cinnamon together in a medium bowl.
Cut in the butter with a pastry cutter (or fork) it forms small pebble-sized crumbs.
Chill the crumb topping while you make the muffin batter.
To make the muffins, preheat oven to 375 F. Grease a standard 12-cup muffin tin with nonstick baking spray or line with muffin liners. I like to use a baking spray with flour or parchment paper liners.
In a large bowl, mash the bananas until well-mashed.
Stir in the melted butter and sugars until well-combined.
Add the egg and vanilla, and mix in until combined.
Stir in the flour, baking soda, baking powder, and salt just until combined.
Divide the muffin batter among the prepared muffin tin cups.
Sprinkle the crumb topping over the batter.
Bake for 15-20 minutes, or until a wooden toothpick inserted in the center comes out clean.
Let the muffins cook in the pan for 5-10 minutes and then remove to a wire rack to finish cooling.