Making Banana Cake Layers

1. Preheat oven’s to 350°F. Line three 6” round cake pans with parchment paper. Alternatively, you can generously butter and flour them or use non-stick baking spray before setting them aside.
2. To a large mixing bowl, add and whisk together the following dry cake ingredients: all-purpose flour, baking powder, baking soda, kosher salt, cinnamon, and nutmeg. Set aside.  
3. Using the paddle attachment in the bowl of a stand mixer, cream your butter and sugars together on medium-high for 2-3 minutes. Stop mixer and scrape down the sides of the bowl. Add the egg and mashed bananas, and mix on medium-high again for 2-3 minutes. You may need to cover your stand mixer with a towel to avoid splatter.   
4. Add your buttermilk, oil, and vanilla extract to one small bowl and drizzle it down the side of the mixing bowl to slowly incorporate it. Start the mixer on a low speed before increasing to medium-high and beating for 4 minutes, until mixture is completely homogeneous with no streaks in the batter.
5. Incorporate dry ingredients into wet for about 30 seconds with your mixer. Continue incorporating by hand with a spatula until well-combined. Scrape the bowl’s sides to ensure no dry ingredients are hiding in pockets.
6. Pour and evenly spread the batter into your prepared cake pans. Bake for 30 - 35 minutes. You’ll know your cake is done when it appears buttery and dense but bounces back at the touch of your finger.
7. Transfer to a wire rack to cool completely.

Making Chocolate Cream Cheese Frosting

1. Create a double boiler on your stovetop, using a medium-sized heatproof bowl on top of a similarly sized pot full of gently boiling water. Pour your heavy cream and chocolate pieces into the heatproof bowl and whisk continuously until smooth.
2. Then pour that into your mixing bowl, along with room temperature cream cheese and vanilla extract. Mix everything together for about 1 minute. It will look initially lumpy.
3. Lastly, beat in powdered sugar last. The final texture will look like a thick pudding. 

Assembling Cake Layers

1. First, pipe or spread a dollop of your frosting onto a cake circle to act as glue to hold the layer in place. Set first cake layer on top of that.
2. With a spoon or offset spatula, evenly spread roughly 20% of your chocolate frosting on top of the bottom layer.  Place second cake layer on top of the first, repeating the same steps, and then add your third layer.
3. Then, starting from the base of the cake, begin to place dollops of frosting onto your cake and drag it around with a spoon or offset spatula. The design is more rustic so doesn't need to be perfect, though be careful to avoid pulling lots of crumbs through your frosting.
4. Continue coating cake with remaining cream cheese frosting.
5. If desired, add sprinkles on top of your cake for a more dressed up appearance.