9 Tablespoons Unsalted Butter, at room temperature
1 cup Sugar
4 ripe Bananas, peeled and mashed
1/3 cup Sour Cream
1 1/4 cups Flour
3/4 teaspoon Baking Soda
1 1/2 teaspoons Baking Powder
3/4 teaspoon Kosher Sea Salt
6 Egg Whites
1 1/2 cups Light Brown Sugar
1 pound Salted Butter (4 sticks - 32 Tablespoons), at room temperature
2/3 cup Malted Milk Powder
2 teaspoons Vanilla
Preheat the oven to 350.
FOR THE CAKE:
In a small bowl, puree together, with an immersion blender or other tool, mashed bananas and sour cream. Set aside for later.
In another bowl whisk together dry ingredients: flour, baking soda, baking powder and salt.
In the bowl of a stand mixer, or in a bowl with an hand mixer, beat together butter and sugar until light and fluffy. About 3-5 minutes.
Alternate adding in flour and banana mixture until fully incorporated into a smooth batter.
Grease and flour two 9" cake rounds, or line with baking parchment.
Divide cake batter between pans.
Bake at 350 degrees for about 30-35 minutes, until a toothpick comes out clean on doneness check.
Let cakes rest 5 minutes, then turn out cakes to cool on a cooling rack.
FOR THE BUTTERCREAM:
Fill a medium saucepan with 2-3 inches of water, and bring to a boil over high heat. Once boiling, reduce to a simmer.
Combine egg whites (reserving yolks for another use) and light brown sugar in the metal mixing bowl of a stand mixer (or if not using a stand mixer another metal bowl) and place over the simmering water.
Whisk while heating until the sugar is dissolved and mixture temperature reaches 180 degrees (measure temperature with a candy thermometer, or other kitchen thermometer).
Using a whisk attachment on a stand mixer (or hand mixer) whisk egg whites and sugar on high until they double in volume. Mixture will be thick and shiny.
Reduce speed to medium and begin to add butter about a 1/2 tablespoon at a time, until all the butter is incorporated. It is important that the butter be room temperature and that you allow it to fulling incorporated between each mix in.
Once all the butter is incorporated, slowly beat in malted milk powder.
Beat in vanilla.
NOTE: If mixture looks broken, increase speed to high and whisk until smooth. If the mixture looks too lumpy, the butter is too cold, applying heat to the bowl while mixing will help smooth it out. You can apply heat with a torch or holding a hot pot against the side of the bowl while it mixes. If the mixture looks too runny, then the butter is melted. You can remedy that by holding an ice pack against the bowl while it mixes. You will see the frosting tighten up. This may seem fussy, but the texture of this cream filling is worth it!
Cut one of the cake halves to flatten the top. This will be for the bottom cake layer.
Cover the top of the bottom layer cake with buttercream.
Place second cake layer over buttercream.
Frost entire cake with cream cheese buttercream.