Banana Sour Cream Coffee Cake

Preheat the oven to 350ºF (180ºC). Lightly grease an 8x8-inch baking dish or line it with parchment paper and set aside.

In a large mixing bowl, cream the softened butter and sugar with a hand mixer until the mixture is pale and fluffy. Add the mashed banana, egg, sour cream, and vanilla extract and mix on medium speed until combined. Set aside.

In a medium mixing bowl, whisk the flour, baking powder, baking soda, cinnamon, and salt until combined. Add dry ingredients to the wet mixture and mix on low speed just until combined.

Pour the cake batter into the prepared baking dish and spread it into an even layer. Set aside.

In a small mixing bowl, stir the dry crumble topping ingredients together, then add the melted butter. With a fork, gently fold the butter into the dry ingredients. It will become crumbly with small and large crumbs. Top the cake batter with the crumb topping mixture.

Bake for 30-35 minutes or until a toothpick inserted into the center comes out with a few moist crumbs (but no liquid batter). If the cake browns too quickly, place foil over the top and continue baking. Allow to cool for at least 10 minutes before serving.