Spray a 9 x 13 baking dish with nonstick cooking spray. Set aside.
In a medium bowl, stir together flour, baking powder and salt. Set aside.
In a separate mixing bowl, mash bananas well. Mix in butter until combined
Then add in sugar eggs and vanilla and mix well.
Slowly stir in flour mixture and milk until combined (alternating the milk and flour until it is all incorporated.)
For the crumble topping & filling: In a medium bowl, combine flour, brown sugar and cubed cold butter using a fork, pastry cutter or your hands. It should start to look almost like sand with coarse crumbs.
Pour half of the banana batter into the prepared baking dish.
Then top the batter with half of the crumb mixture.
Then pour the last half of the banana batter on top of the crumb mixture.
Finally, layer the last of the crumb mixture on top.
Bake for about 50-60 minutes until the center is set and a toothpick comes out clean.
While it is cooling, make the glaze topping.
Whisk together powdered sugar and milk until smooth. Drizzle glaze all over crumb cake.
This cake can be served warm or at room temperature. It does not need to be refrigerated but make sure you put a lid on it or cover with plastic wrap to keep it moist.