Preheat the oven - Set the oven rack in the middle of the oven and preheat to 350°F.
Prepare the baking pan - Brush your baking pan with melted butter or nonstick baking spray and line it with a piece of long parchment paper, allowing the excess to hang over the sides. Brush the parchment paper with additional melted butter. Set aside.
Prepare wet ingredients for chocolate banana cake - Mash the bananas with a potato masher in a large mixing bowl. Add oil, eggs and vanilla, and beat with a whisk until thoroughly combined.
1 ⅓ cup mashed banana, 3 oz vegetable or canola oil, 2 large eggs, 1 teaspoon pure vanilla extract
Add sugar - Add brown sugar and beat again until completely incorporated.
1 cup brown sugar
Add dry ingredients - Sift flour, cocoa powder, baking soda and baking powder into another small mixing bowl. Add the salt and mix to distribute evenly. Add the dry ingredient mixture into the bowl with the wet ingredients. Mix gently with a whisk or a spatula until combined and no trace of flour remains.
1 cup all-purpose flour, ½ cup cocoa powder, ½ teaspoon baking soda, ½ teaspoon baking powder, ½ teaspoon kosher salt
Bake - Transfer the cake batter to the prepared baking pan and bake in the preheated oven for approximately 35 minutes, until a toothpick inserted into the center of the cake comes out clean with just a few crumbs attached.
Cool - Remove the cake from the oven and let cool completely on a wire rack before adding frosting.
Make the miso caramel frosting - Add softened butter and ½ cup of miso caramel to a stand mixer bowl fitted with the whisk attachment. Beat on medium speed for just a couple of minutes until the mixture is thoroughly combined and creamy.
8 oz unsalted butter, ¾ cup miso caramel
Add sugar and beat until fluffy - Add powdered sugar and stir to combine. Then gradually increase the mixer speed and beat until the frosting is lighter in color and fluffy, about 5 minutes.
1 cup powdered sugar
Add frosting to the cake - Spread miso caramel frosting evenly on top of the cooled cake with an offset spatula to cover the entire surface of the cake.
Add caramel drizzle - Add the remaining ¼ cup of miso caramel to a pastry bag or a ziploc bag. Snip the corner and drizzle caramel over the frosting. Slice and serve!
¾ cup miso caramel
Notes
Miso caramel substitution: warm up ¾ cup of any caramel sauce (homemade or store bought), mix in 1 tablespoon of white miso paste using a small spatula. Let it cool and use as the recipe directs. I use Marukome premium white miso paste.
Yield: this cake can serve up to 12 people or 9 for more generous portions.
Storage: you can refrigerate your chocolate banana cake in an airtight container for 3-5 days. Or you can wrap leftovers individually and freeze for up to 3 months. Let it come up to room temperature a bit before serving.