Preheat the oven to 350°F. Grease a 10 x 15-inch (also known as a jelly roll pan) sheet pan and set it aside.

In a large bowl, combine the brown sugar, white granulated sugar, and butter. Using a stand mixer, hand mixer, or whisk, cream the mixture until it is light and fluffy, 3 minutes. Add the egg, vanilla extract, and mashed banana. Beat the mixture until it is combined.

Add the flour, baking powder, and salt. Mix until the dry ingredients are just combined, but do not over-mix. Fold the chocolate chips into the batter.

Pour the batter into the prepared sheet pan and place in the preheated oven. Bake until the bars are golden and a skewer inserted into the middle comes out clean, 30-40 minutes. Let cool completely before icing.

Once the bars are cooled, spread on the icing, covering the bars completely. Slice and serve.

Beat the cream cheese and butter until light and fluffy. Add the vanilla extract, salt, and sifted powdered sugar. Slowly mix in the sugar until it is smooth.

Add more sugar to thicken or milk to thin the frosting.