Preheat oven to 350° F. Grease two 6" cake pans (see note) and set aside.
Mash bananas and set aside.
In a medium bowl, combine the dry ingredients (flour, baking powder, baking soda, and salt). Set aside.
In the bowl of a stand mixer, combine butter and sugar. Beat until light and fluffy. Scrape down the sides of the bowl as needed.
Add eggs one at a time, then the vanilla. Mix to combine.
With the mixer running on low speed, add half the dry ingredients, followed by the sour cream, then the remaining dry ingredients. Mix until just incorporated, then fold in mashed bananas.
Divide the batter evenly between the prepared pans. Bake 35-45 minutes, or until a toothpick inserted in the center comes out clean. (Bake time will vary a bit based on the size of your bananas...just make sure to check the cakes often starting at the 30-minute mark.)
Cool the cakes in the pan for 10 minutes, then turn them out onto a wire rack to cool completely.
For Frosting:
In the bowl of a stand mixer, combined butter and cream cheese. Beat until smooth. Scrape down the sides of the bowl as needed.
Add espresso powder and mix to combine. Then add powdered sugar and mix until combined.
For Assembly:
Split the two cakes, so that you have four layers total. Frost the cake, adding cocoa nibs and grated chocolate between the layers. After frosted, top with cocoa nibs, grated chocolate, chocolate-covered espresso beans, and freeze-dried bananas.Enjoy!
Notes
Note on espresso powder: I've found it difficult to find espresso powder--especially one that isn't already hard as a rock--at my local grocery store. I use King Arthur Flour's brand (link [here]), as it's very fine and made specifically for baked goods.Note on cocoa nibs: Cacao nibs can be tricky to find. I've scored them before at HomeGoods <3 , but you can't count on them being there consistently. I've never seen them in a grocery store. If you can't find them, you can find them online [here].Note on cake pans: This recipe is for a 6" four-layer cake. If you're looking to get some 6" pans for yourself, these are the ones that I use [here]. Note on freeze-dried bananas: If you can't find them in the grocery store, you can find them [here]. Also note that if you garnish the cake in advance, the bananas will lose their crunch. I suggest placing the bananas on top just before serving.Note on chocolate-covered espresso beans: This is another hit-or-miss item at the grocery store. I bought mine online [here].