Preheat your oven to 350°F (175°C). Grease a 9" x 13" baking dish with butter or cooking spray and set it aside.

In a large bowl, combine the cold butter cubes, flour, brown sugar, granulated sugar, and cinnamon. Use your hands or two forks to mix until the mixture resembles a crumbly topping. Set this crumb mixture aside.

In another large bowl, whisk together the flour, baking powder, cinnamon, and salt. This ensures an even distribution of the leavening agents.

In a stand mixer, beat the softened butter on medium speed until creamy, about 2 minutes. This step is crucial for a fluffy cake.

Add the granulated sugar and mix for another minute until well combined. Then, add the eggs, vanilla, and mashed bananas, mixing just until incorporated (be careful not to overmix!).

Reduce the mixer speed to low and alternate adding the milk and flour mixture until everything is combined. This helps prevent overmixing and keeps your cake tender.

Pour half of the cake batter into the prepared baking dish. Sprinkle 1/3 to 1/4 of the crumb mixture on top for a delightful crunch.

Pour the remaining cake batter over this layer, and finish by topping it evenly with the remaining crumb mixture. This layering creates a beautiful presentation.

Bake in the preheated oven for 50-55 minutes, or until a toothpick inserted into the center comes out clean. Keep an eye on it as baking times may vary!

If you want to make the optional glaze, whisk together the powdered sugar and 1 tablespoon of almond milk in a small bowl. Add more milk as needed to achieve your desired glaze consistency.

Allow the cake to cool at room temperature for 5-10 minutes before drizzling the glaze over the top. Slice and serve! Enjoy your homemade banana crumb cake!