Preheat oven to 375 degrees. Use muffin papers or grease 12 muffin cups.

Prepare topping: In a small bowl combine brown sugar, 2 tablespoons flour, and cinnamon.  Use your fingers to break up the 1 tablespoon butter and then crumble it with your fingers until it looks like wet sand.  Set aside.

Prepare Muffins:  In a small bowl, smash your bananas until you measure out 1 1/2 cups.  (*the number of bananas is simply a suggestion of how many it might take, never use that number in banana recipes, always measure it out.) Set aside.

Place 1/3 cup butter in your mixing bowl and place in the microwave to melt.  Add sugar and egg and use a hand mixer to combine.  Mix in mashed bananas.

Add flour to bowl (but don't mix it in yet). Sprinkle baking powder, baking soda, and salt over the flour.  Use mixer to mix everything together.  Don't beat your batter too much, just mix until all of the dry ingredients are incorporated.

Fill muffin cups about 2/3 - 3/4 full.  I generally have a bit extra batter. If you have another muffin pan you can fill just a couple more,  or bake a few mini muffins, or put it in a mini-mini loaf pan.

Sprinkle topping over all of your muffins and then bake for 15-20 minutes, until a toothpick comes out with just a few moist crumbs attached.