For the Banana Cake

• Preheat the oven to 350 and line a 9 inch square baking pan with parchment paper.
• In a large mixing bowl (or a stand mixer) cream the butter and sugar until well combined.
• Add the egg and vanilla and mix until the egg is fully incorporated.
• Mix in the mashed bananas.
• In a separate bowl, whisk together the flour, baking powder, baking soda, and salt.
• Add 1/2 of the dry ingredients to the mixing bowl and mix until just combined.
• Add the buttermilk and mix to combine.
• Finally, add the remaining 1/2 of dry ingredients and mix until just combined, being careful not to over mix.
• Pour the batter into the prepared pan and smooth into an even layer with an offset spatula. Bake at 350 for 25 minutes, or until a toothpick comes out mostly clean with a few moist crumbs attached.
• Let cake cool in the pan for 10 minutes, then lift it out onto a cooling rack to cool completely before frosting.

For the Peanut Butter Cream Cheese Buttercream

• In a medium mixing bowl, cream the butter and cream cheese until they are well combined and smooth. Make sure to scrape down the bottom and sides of the bowl to make sure there’s no clumps of cream cheese.
• Add the peanut butter and vanilla and mix to combine. 
• Add the powdered sugar and mix on low until smooth.
• Add heavy cream 1 TBSP at a time until you reach your desired consistency. Look for soft and spreadable, but still thick enough to hold its shape.
• Spread the frosting onto the cooled banana cake in an even layer.
• Melt 2 TBSP of peanut butter.
• Dollop melted peanut butter and marshmallow fluff all over the top and use a spoon to swirl it into the buttercream.
• Slice into 16 squares and enjoy.