Spray a 9 x 13 baking pan with cooking spray and preheat oven to 350.
In a medium bowl, combine the flour, baking powder, and salt. Set aside.
In a large bowl, mash the bananas until they become liquefied.
Mix in the butter until combined and stir in the sugar, eggs, and vanilla.
Stir in the flour mixture and milk.
In a separate bowl, combine the cold butter, light brown sugar, and flour.
Cut them together using two forks or a pastry blender until coarse crumbles form.
Pour half the cake batter into the greased pan followed by 1/2 the crumb topping.
Pour remaining batter on top of crumb topping, ended with remaining topping.
Place pan in oven and bake for 55 minutes, or until center is set.
Remove from oven and allow to cool for about 10 minutes before serving!