Preheat oven to 350 degrees.
Spray muffin top pan with non-stick cooking spray.
In large bowl mash bananas with fork. Add melted butter and mix with fork until smooth.
Stir in sugar, egg, and vanilla.
In small bowl whisk together flour, baking soda, and baking powder. Add to banana mixture and mix until just combined.
Fill muffin top wells half full.
For the crumb topping: Mix brown sugar, granulated sugar, cinnamon and salt in a medium bowl.
Add the melted butter and mix with a fork.
Add the flour and mix until clumps form.
Top the muffin top batter generously with the crumb topping.
Bake at 350 degrees for 15 minutes.
Remove from oven and cool in pan on wire rack.
Remove from pan and sprinkle with confectioner's sugar if desired.