Pre-heat oven to 350 F and line a muffin tin with cupcake wrappers.

Muffin Base-

Combine the flour, baking powder, baking soda, and salt in a small mixing bowl.

In a large mixing bowl combine the mashed bananas, sugar, brown sugar, sour cream buttermilk, oil, egg, and vanilla till thoroughly mixed. Dump the flour mixture into the wet mixture and stir with a wooden spoon till just barely mixed together. Don’t overmix.

Filling-

In a small bowl, combine the cinnamon and brown sugar to make the filling.

Crumb Topping-

In another small bowl combine the flour, brown sugar, sugar, cinnamon. Pour in the melted butter and mix using a fork. Try to mix it till there are still some medium size clumps left.

Assembly-

Fill each muffin tin 1/3 full with muffin batter. Sprinkle about ½ teaspoon of the filling over each muffin. Scoop more batter into each tin till it is about 2/3 full. Sprinkle the topping so it covers a majority to all the muffin batter.

Place on a middle rack of your oven and bake for 14-18 minutes till a toothpick inserted comes out with a few moist crumbs. Let muffins cool in muffin tin for 5 minutes before removing to cool on a cooling rack.

Icing Drizzle-

Whisk together the powdered sugar, milk, and vanilla extract till creamy. Once the muffins are cool drizzle the icing over each muffin.

Store in an airtight container for up to 4-5 days.