Preheat your oven to 350°F. Grease a 15x10x1-inch baking pan lightly, or line it with parchment paper for easy removal.
In a large mixing bowl, cream the butter and sugar together using a hand or stand mixer. Beat on medium-high for 5-7 minutes until light and fluffy.
Mix in the eggs one at a time, followed by the sour cream and vanilla extract. Stir well to combine.
In a separate bowl, whisk together the flour, baking soda, and salt. Gradually add this dry mixture to the wet ingredients, mixing on low to avoid overworking the batter.
Fold the mashed bananas gently into the batter until fully incorporated. Avoid over-mixing to keep the bars tender.
Spread the batter evenly into the prepared pan. Bake for 20-25 minutes, or until a toothpick inserted in the center comes out clean. Allow the bars to cool completely in the pan.
Prepare the frosting by combining cream cheese, butter, and vanilla extract in a mixing bowl. Beat on medium speed until fluffy.
Gradually add the confectioners’ sugar 1 cup at a time, mixing until the frosting reaches your desired consistency.
Once the bars have cooled, spread the frosting generously over the top. Slice into bars and serve.