Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking pan.

Mash 3 spotty bananas until mostly smooth.

Add softened butter and brown sugar to the bananas and mix until creamy.

Beat in 2 room-temperature eggs one at a time, along with 1 teaspoon of vanilla extract.

Whisk together 2 cups of all-purpose flour, 2 teaspoons of baking powder, and 1/2 teaspoon of salt.

Gradually add the flour mixture to the wet ingredients, alternating with 1/2 cup of milk.

For the crumb topping, mix together 1/2 cup of cubed cold butter, 1/2 cup of brown sugar, and 1/2 cup of flour.

Pour half of the banana batter into the greased baking pan, spread it evenly, and sprinkle half of the crumb topping.

Add the remaining banana batter and top with the rest of the crumb mixture.

Bake for approximately 50 minutes or until a toothpick comes out clean.

Cool for 10-15 minutes before serving.