Preheat the Oven: Begin by preheating your oven to 350°F (175°C). Grease and line two 9-inch cake pans with parchment paper to ensure easy removal later.
Prepare the Dry Ingredients: In a medium bowl, whisk together the all-purpose flour, cocoa powder, baking soda, baking powder, and salt. This step ensures that your dry ingredients are nicely combined before incorporating them into the batter.
Mix the Wet Ingredients: In a large bowl, beat together the eggs, granulated sugar, buttermilk, vegetable oil, and vanilla extract until smooth. Stir in the pureed bananas for that added richness.
Combine Wet and Dry Ingredients: Gradually add the dry ingredients to the wet mixture, stirring until just combined. Be careful not to overmix—the batter should be smooth with a few small lumps.
Bake: Divide the batter evenly between the prepared pans and smooth the tops. Bake in the oven for about 30-35 minutes, or until a toothpick inserted into the center comes out clean.
Cool: Once baked, remove the cakes from the oven and let them cool in the pans for about 10 minutes. Then, turn them out on wire racks to cool completely.
Make the Frosting: In a large bowl, beat the softened butter until creamy. Gradually add the powdered sugar and cocoa powder, mixing well. Then, add the heavy cream, vanilla extract, and a pinch of salt, beating until fluffy and smooth.
Assemble the Cake: Once the cakes are completely cool, place one layer on your serving plate and top it with a generous amount of frosting. Add the second layer and frost the top and sides of the cake evenly.
Garnish and Serve: For the finishing touch, garnish with chocolate shavings and banana slices if desired. Let the cake rest for about 30 minutes before slicing—this enhances the flavors.