1-Preheat oven to 350F degrees: Preheat oven to 350F degrees. Spray a 9 x 13 baking dish with nonstick cooking spray. Set aside.
2-In a medium bowl, stir together flour,: In a medium bowl, stir together flour, baking powder and salt. Set aside.
3-In a separate mixing bowl, mash bananas: In a separate mixing bowl, mash bananas well. Mix in butter until combined.
4-Then add in sugar, eggs and vanilla: Then add in sugar, eggs and vanilla and mix well.
5-Slowly stir in flour mixture and milk: Slowly stir in flour mixture and milk until combined (alternating the milk and flour until it is all incorporated.)
6-In a medium bowl, combine flour, brown: 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.
7-Pour half of the banana batter into: Pour half of the banana batter into the prepared baking dish.
8-Then top the batter with half of: Then top the batter with half of the crumb mixture.
9-Then pour the last half of the: Then pour the last half of the banana batter on top of the crumb mixture.
10-Finally, layer the last of the crumb: Finally, layer the last of the crumb mixture on top.
11-Bake for about 50-60 minutes until the: Bake for about 50-60 minutes until the center is set and a toothpick comes out clean.
12-Whisk together powdered sugar and milk until: Whisk together powdered sugar and milk until smooth. Drizzle glaze all over crumb cake.