Step 1

Preheat oven to 350°F. Grease a 9x9-inch baking pan and line with parchment paper, leaving an overhang on the sides.

Step 2

Make the cake. In a medium bowl, whisk flour, baking powder, baking soda, and salt. Set aside.

Step 3

In a separate large bowl, beat the butter and sugars with an electric mixer until creamy, about 2-3 minutes. Scrape the bottom and sides of the bowl, as needed.

Step 4

Add the eggs and mix until well blended. Stir in the mashed bananas and the vanilla. Then, alternate adding the dry ingredients and sour cream, stirring by hand until just combined.

Step 5

Pour half of the batter into the prepared pan. Combine the cinnamon and sugar in a small bowl and sprinkle evenly over the batter. Then, dollop and gently spread the remaining batter over the top. Set aside.

Step 6

Make the streusel. In a small bowl, combine the flour, brown sugar and cinnamon. Cut in the cold butter with a pastry blender or rub it between your fingers until the mixture resembles coarse crumbs. Sprinkle the streusel evenly over the batter in the pan.

Step 7

Bake for 40-45 minutes, or until a toothpick inserted into the center comes out clean. If the top is browning too quickly, tent with aluminum foil.

Step 8

Take the cake out of the oven and leave to cool in the pan for 15 minutes. Then lift it out with the parchment overhang and place it on a wire rack to cool fully.

Step 9

Make the glaze. In a small bowl, mix the powdered sugar with 2 tablespoons of milk and the vanilla until smooth. Add more milk, if needed, until it’s thick but pourable.

Step 10

Drizzle the glaze over the cooled cake, let it set, then slice, serve, and enjoy!