Preheat your oven to 350°F (175°C). Grease and flour a 9-inch round cake pan or line it with parchment paper. This helps your cake come out clean and prevents sticking.

In a large bowl, whisk together the all-purpose flour, cocoa powder, baking soda, baking powder, and salt. Set aside. This dry mix will give your cake that rich, chocolatey base.

Mash the bananas in a separate bowl until smooth. In another large bowl, combine the mashed bananas, oil or melted butter, brown sugar, and granulated sugar. Whisk in the eggs, one at a time, followed by the sour cream. You want everything to be smooth and well combined.

Slowly add the dry ingredients to the wet mixture, stirring gently until everything is just combined. Don't overmix, as that can make the cake dense. You'll want to keep the batter light and fluffy.

Pour the batter into the prepared cake pan. Bake for about 30-35 minutes or until a toothpick inserted in the center comes out clean. Let the cake cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.

While the cake is cooling, let’s get that decadent frosting ready. In a large bowl, beat together the softened butter, cream cheese, and peanut butter until smooth. Add the vanilla extract and salt, then gradually sift in powdered sugar, starting with 2 cups. Beat until smooth and creamy. You can add more powdered sugar if you like your frosting sweeter or thicker.

Once the cake is completely cool, spread a generous layer of frosting over the top. You can decorate it with some banana slices or chocolate shavings for extra flair. Slice it up, serve, and enjoy!