Preheat the oven to 350 degrees and grease a 8x8 pan. Lay a square of parchment paper in the bottom of it.
Roast the bananas in the oven with the peels on for approximately 30 minutes. Let cool while preparing the batter.
In a saucepan, add the butter and sugars. On medium heat, let the butter melt and whisk occasionally.
Once the butter is melted, whisk until everything comes together. It will be a brown color and thick consistency.
Once the sugars and butter are combined, remove from the heat to cool.
After 2-3 minutes of cooling, add the butter/sugar mixture into a mixing bowl. I placed mine in my stand mixer with a whisk attachment.
Add the walnut butter and whisk until combined.
Add one egg at a time and whisk until incorporated. Be sure to scrape down the sides. Repeat with the other egg.
Peel the three bananas into the mixing bowl. I make sure I get all the juice in the bowl too. Discard the peels. Whisk until combined. Small bits of the banana strings may stick to your whisk. I leave them on there and discard them after the batter is mixed.
In a separate bowl, sift together the flour, salt, and baking soda.
Add the dry ingredients into the batter and give a whisk just until there is no more flour apparent.
Pour into the 8x8 baking pan and give it a tap to get the air bubbles out.
Bake for 28 - 30 minutes minutes or until it's done. A toothpick should come out without any batter on it. It's okay if there are some crumbs stuck to the toothpick.
Frosting
In your stand mixer or mixing bowl with hand mixer, mix the softened cream cheese and butter together until incorporated very well.
Add the brown sugar and mix for 2 minutes.
Add the vanilla and give it another whip until combined.
Add the powdered sugar and mix on low so the sugar doesn't fly every where. Once most of the sugar is combined, mix on medium. Whip it until it is fluffy.
Let cool in the pan for 10 minutes. Turn out onto cooling rack to finish cooling.