Preheat oven to 350F. Grease an 8 inch square pan and line it with overhanging parchment paper.
In a medium-sized bowl, whisk together the flour, cinnamon, baking soda and salt. Set aside.
In a large mixing bowl, use an electric mixer set to medium-high to cream together the granulated sugar, brown sugar and butter until light and fluffy (about 2-3 minutes).
Beat in the egg and vanilla, then mix in the mashed banana.
On low speed, gradually add the flour mixture and milk to the wet mixture, alternating between them both, until just combined. The batter should be smooth. Be careful not to over mix.
Pour the batter into the prepared pan and use an offset spatula to spread out evenly. Gently tap the bottom of the pan off the counter to help release any air bubbles.
Bake for 27-29 minutes, or until a toothpick inserted into the center comes out clean.
Let cool on a wire rack before frosting.
To make the frosting, add the cream cheese, butter and peanut butter to a mixing bowl and use an electric mixer on medium-high speed to cream together. Gradually add the powdered sugar until the frosting is smooth and creamy.
Spread the frosting onto the cooled cake, slice and serve.
Store in an airtight container in the fridge for up to 5 days.
Notes
If you don’t have a kitchen scale to weigh your flour, be sure to measure it using the spoon and level method with a dry measuring cup.
Make sure you cream together the butter and sugars for a good 2-3 minutes so they are light and fluffy.
For the best results, use shelf stable smooth peanut butter in the frosting. Natural peanut butter will make the frosting too runny.
For a thicker and sweeter cream cheese frosting, just add more powdered sugar.
To make this recipe dairy-free, you can substitute the butter, cream cheese and milk for plant-based alternatives.