Preheat the oven to 350 degrees F. Line a 9x13-inch baking pan with parchment paper, set aside.
In a medium sized bowl, whisk together the flour, baking powder, and salt, set aside.
In a large bowl add the melted butter, brown sugar, mashed banana, egg, and vanilla, whisk until smooth.
Next, add the flour mixture and stir until combined, making sure there are no dry patches remaining..
Spread the batter into the prepared baking pan and bake for 30-35 minutes until the edges are slightly golden brown and a toothpick inserted into the center comes out clean. Place the baking pan on a wire rack to cool completely, this helps air get under the pan and cool quicker.
Next make the frosting, place the cream cheese and butter into a large bowl and with an electric hand mixer beat until smooth.
Add the powdered sugar a little at a time until combined, scraping down the sides as needed. Add in the vanilla and turn the mixer on to medium speed and beat for 3 minutes until light and fluffy.
Remove the blondies out of the baking pan by lifting the parchment paper to help grab and remove. Frost blondies, cut into bars and serve immediately.