1and 1/2 cups mashed banana(4 medium ripe bananas or 3 large ripe bananas)
1/2cup(120 ml) buttermilk
To make the crumb topping:
In a large mixing bowl, whisk together the flour, brown sugar, and cinnamon. Cube the cold butter into small pieces and add to the flour mixture. Using a pastry blender (or your hands) cut the butter into the mixture until it starts to clump together and is crumbly. Transfer to the refrigerator while you make the cake batter.
To make the cake:
Preheat oven to 350°F. Spray a 9-inch springform pan with non-stick cooking spray and set aside.
In a large mixing bowl, whisk together the flour, baking powder, baking soda, cinnamon, and salt. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, or in a large mixing bowl using an electric mixer, cream together the butter, brown sugar, and granulated sugar for 2-3 minutes until well combined. Mix in the eggs, vanilla extract, and mashed banana, making sure to mix well after adding each ingredient.
Slowly add the dry ingredients in three additions, alternating with the buttermilk, and mixing each addition just until combined.
Scoop the batter into the prepared springform pan. Remove the crumb topping from the refrigerator and sprinkle on top of the batter.
Bake at 350°F for 50-60 minutes or until a toothpick inserted into the center of the cake comes out clean. Cover loosely with foil for the last 10-15 minutes of baking if needed to prevent excess browning.
Remove from the oven and transfer to a wire rack to cool for at least 30 minutes before removing from the springform pan. Allow to cool completely before serving.
Storage instructions: Store banana cake on the counter in an airtight container for up to 2 days.