Banana Cake with Chocolate Frosting

Name: Banana Cake with Chocolate Frosting
Prep time: 20 min
Cook time: 35 min
Total time: 55 min
Ingredients: ½ cup unsalted butter; 1 cup bananas (mashed); ½ cup light brown sugar; ¼ cup white sugar; 2 teaspoons vanilla extract; 2 large eggs (room temperature); ¼ cup buttermilk (room temperature); 1 teaspoon baking soda; ½ teaspoon baking powder; ½ teaspoon ground cinnamon; ½ teaspoon kosher salt; 1 ¾ cup all purpose flour; 3 oz dark chocolate (chopped); ½ cup unsalted butter (room temperature); 1 cup confectioners' sugar; ½ cup cocoa powder; ¼ cup sour cream (room temperature)

This extra moist banana cake with chocolate frosting is the perfect recipe for when you've got some extra overripe bananas! The cake is made in 1 bowl without a mixer, and it's topped with a luscious chocolate sour cream frosting.

Squares of banana cake with chocolate frosting on parchment paper.

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After making my chocolate walnut snack cake, I knew I needed to make another snack cake! This fluffy and moist banana cake is topped with the same chocolate sour cream frosting. This is my favorite frosting, it is so creamy and rich!

If you want more of a classic banana bread recipe, try out my banana bread with chocolate chunks! I ended up using this cake as a base for my banana cake with peanut butter frosting.

Why you'll love this recipe!

This banana cake is basically a cake version of banana bread! It's a one layer cake with a thick layer of chocolate frosting.
This is the perfect recipe for when you've got a few too many overripe bananas.
The cake is made in 1 bowl and you don't need a mixer.
The frosting can be made in advance, you'll just need to let it warm up before spreading on top of the cake.

Ingredients Needed

Bananas: make sure to use overripe bananas that have dark spots on them, those will be sweeter and easier to mash!
Flour: I've only tested this recipe with all purpose flour.
Buttermilk: this is going to keep the banana cake extra moist! You can substitute it with sour cream if you don't have buttermilk on hand.
Unsalted Butter: you'll need butter for both the banana cake and the frosting!
Cinnamon: I like a slightly spiced banana cake, but if you aren't a fan of cinnamon then you can leave it out.
Cocoa Powder: I've used unsweetened cocoa powder here, but you could use dutch processed cocoa powder in a pinch!

Step by Step Instructions

Steps 1 and 2 in the banana cake baking process.

Step 1: Preheat the oven to 350°Fahrenheit/175°Celsius. Melt your butter in a large microwave safe bowl. Once cooled, add your mashed banana. Whisk to combine.

Step 2: Pour in the white sugar and light brown sugar, whisk for 1 minute. Add the two eggs, buttermilk and vanilla extract. Whisk again to combine. It is going to be a bit lumpy because of the banana which is fine!

Steps 3 and 4 in the banana cake baking process.

Step 3: Use a rubber spatula to fold in all of the dry ingredients - the flour, baking powder, baking soda, salt and cinnamon. Fold until there are no more pockets of flour left in the batter.

Step 4: Pour into a greased and line 8x8 baking pan. Bake for 30-35 minutes, a toothpick inserted should come out clean or with a few crumbs. Let it cool in the pan for 20 minutes, then lift it out of the pan and let it cool completely on a wire cooling rack.

Steps 5 and 6 in the banana cake baking process.

Step 5: In the bowl of a stand mixer fitted with the paddle attachment, or in a large bowl with a handheld mixer, beat the softened butter and confectioners' sugar together on low speed until it is combined. Then increase the speed to medium-high and beat for 2 minutes.

Step 6: Pour in the cocoa powder and beat until it has combined with the butter on low speed, then increase to medium speed for 2 minutes. Pour in the (cooled!) melted chocolate and sour cream, mix once more. Spread on top of the cooled cake.

A square banana cake topped with chocolate frosting and banana slices.

Baking Tips & Tricks

Measuring Ingredients - I highly recommend using a weighing scale and measuring out your ingredients the metric way. It makes a huge difference to your baking and is the most accurate way to bake!
Fluffing Flour - If you don't have a weighing scale make sure you're measuring out your flour correctly with measuring cups. I recommend taking a look at this link here on how to fluff and sprinkle flour when measuring!
Ripe Bananas - I really recommend using overripe bananas for this banana cake. They'll be much sweeter and easier to mash up!
Lining the Pan - when lining the pan, make sure there is enough parchment paper on both sides so you can easily lift the cake out once it's been baked!

Frequently Asked Questions

Can I use a round pan instead?

Yes you can! Use a round 9"pan instead of the 8x8 baking pan.

What if I don't have buttermilk?

You can either substitute it for sour cream or make your own buttermilk! It won't be as good as regular buttermilk but it'll do in a pinch. For every cup of buttermilk needed, mix one cup of whole milk with 1 tablespoon of lemon juice. Whisk together then let it sit for 5 minutes before using.

Can I make this ahead of time?

Yes, you can make both elements of the cake a day in advance. Once the cake is cool, wrap it tightly in plastic wrap and store in the fridge. For the frosting, place it in a bowl and cover the surface of the frosting with plastic wrap. Store in the fridge. When ready to frost the cake, take the frosting out and let it sit on the counter for at least 1 hour. If it's still too firm to scoop, I recommend microwaving it for a few seconds until it is spreadable!