Preheat oven to 350 degrees F and coat a 9×5 pan with cooking spray; set aside. Combine the butter, brown sugar, sugar, eggs and vanilla in a large bowl. Mix well.
In a medium bowl, combine flour, baking soda, baking powder and salt and mix well. Gradually add to the butter-sugar bowl until combined. Add mashed bananas. Pour into prepared pan.
In a small bowl, combine the 2 tablespoons of butter, 1/2 cup of flour and 1/2 cup of brown sugar. Mix until crumbly. Spread over the top and bake in the preheated oven for approximately 1 hour.
Start checking for doneness at the 50-minute mark. When a toothpick inserted into the center comes out clean, the bread is done.
Notes
An easy recipe variation would be to make this banana nut bread! A little crunch is delicious. Chop up a cup of walnuts and fold them into the batter.
A cup of chocolate chips or raisins are alternative add-ins.