Preheat the oven to 350 degrees.
In a large mixing bowl, mix butter, brown sugar, vanilla extract, milk, eggs and the bananas. Set aside.
In a medium mixing bowl, mix the flour, baking powder, cinnamon, baking soda and salt.
Slowly mix the dry ingredients into the wet ingredients until the batter forms. Use a hand mixer on low.
Add the batter to a well greased 9x13 baking pan.
In a small mixing bowl, mix the ingredients for the streusel.
Add the streusel to the evenly to the top of the batter. If needed, form into pieces and spread these out over the top of the batter.
Place the baking dish in the oven and cook for 50-60 minutes or until a toothpick comes out clean from the middle.
Serve.