Preheat the Oven: Preheat your oven to 175°C (350°F) and grease or line a 9x13-inch baking pan.
Beat the Butter and Sugars: In a large bowl, cream the softened unsalted butter, granulated sugar, and brown sugar until the mixture is light and fluffy.
Add Wet Ingredients: Beat in the eggs one at a time, then add the vanilla extract and mashed bananas. Mix until well combined.
Combine Dry Ingredients: In another bowl, sift the flour, baking powder, baking soda, and salt together. Gradually add this dry mixture to the wet mixture, mixing just until combined to avoid overmixing.
Incorporate the Sour Cream: Gently fold in the sour cream (or Greek yogurt) until the batter is smooth.
Bake: Pour the batter into your prepared pan and smooth the top. Bake for 30-35 minutes or until a toothpick inserted into the center comes out clean. Allow the cake to cool completely in the pan.
Make the Frosting: In a mixing bowl, beat together softened cream cheese and butter until smooth. Gradually add in the powdered sugar, vanilla extract, and milk, mixing until creamy and well combined.
Glaze and Decorate: Once the cake is completely cooled, spread the cream cheese frosting over the top. If desired, garnish with sliced nuts, bananas, or a drizzle of caramel sauce.