Chocolate Peanut Butter Fun Cake

Ok, ok, I admit that “fun” in the title of the cake is a bit cheesy, but I’ll readily admit another point: this cake really is fun.

The entire dessert is less about the chocolate cake (just make sure you have a classically delicious, moist chocolate cake base) and more about the absolutely divine peanut butter buttercream frosting. While we were eating this tasty treat, Brian and I must have said to each other at least four times, “This frosting is amazing” or “This cake is all about the frosting” or “This cake would be nothing without the frosting.” See how fun our conversation is at the dinner table? We are such fun people, it kills me.

Chocolate Peanut Butter Fun Cake

The buttercream frosting is made using a method similar to a swiss meringue buttercream, which simply means that egg whites are cooked with sugar prior to whipping. The silky texture and crazy-good creamy flavor of the frosting reminded me of this magical frosting, which I have already waxed poetic about in the past. Softer and lighter than traditional buttercream frostings, this peanut butter buttercream was quite simply one of the most delicious concoctions I’ve ever topped a cake with. And it won’t be the last.

Garnished with roasted peanuts and chocolate shavings and you’ve got yourself the funnest cake of the century.

Chocolate Peanut Butter Fun Cake

One Year Ago: Homemade Ciabatta Bread
Two Years Ago: Stir Fry Basil Chicken

Chocolate Peanut Butter Fun Cake

Yield: Serves 9

Chocolate Peanut Butter Fun Cake

Note: I skipped the cake recipe from Bon Appetit and used another chocolate cake recipe I've made and loved before (and that is also baked in an 8X8-inch pan). If you already have a much-loved, tried-and-true 8X8-inch chocolate cake recipe, go ahead and use it. This cake simply needs a delicious chocolate base to convey the tastiness of the silky peanut butter buttercream.


    For the Cake:
  • 1 1/2 cups all-purpose flour
  • 3/4 cup granulated sugar
  • 1/4 cup natural cocoa powder
  • 3/4 teaspoon baking soda
  • 1/2 teaspoon salt
  • 1/3 cup vegetable or canola oil
  • 1 tablespoon distilled white vinegar
  • 1 teaspoon vanilla extract
  • 1 cup water
  • For the Peanut Butter Buttercream:
  • 1/2 cup sugar
  • 1/4 cup egg whites (from about 2 large eggs)
  • 1 1/2 teaspoons vanilla extract
  • 1/4 cup creamy peanut butter
  • 6 tablespoons (3/4 stick) chilled butter, cut into 1/4-inch cubes
  • 1/4 cup chopped semisweet or bittersweet chocolate (about 1 3/4 ounces), for garnish
  • 1/4 cup chopped unsalted, dry-roasted peanuts, for garnish


  1. For the cake, adjust an oven rack to the middle position and heat the oven to 350 degrees F . Coat an 8-inch-square baking pan with nonstick cooking spray.
  2. Whisk the flour, sugar, cocoa, baking soda, and salt together in the baking pan. Make 1 large and 2 small craters in the dry ingredients. Add the oil to the large crater and vinegar and vanilla separately to the remaining small craters. Pour the water into the pan and mix until just a few streaks of flour remain. Use a rubber spatula to spread the batter evenly in the pan if it isn’t level after mixing. Immediately put the pan in the oven.
  3. Bake until a toothpick inserted in the center of the cake comes out with a few moist crumbs attached, about 23-25 minutes. Don’t overbake or the cake will be dry! Remove from the oven and let the cake cool completely in the pan set on a wire rack.
  4. For the buttercream, combine the sugar and egg whites in a medium metal or glass bowl set over a saucepan of simmering water. Whisk constantly until the sugar dissolves and the mixture is hot to the touch, 3–4 minutes. Remove the bowl from off the saucepan and using an electric mixer, beat on high speed until the mixture is cool and thick, 5–6 minutes. Beat in the vanilla, then the peanut butter. With the mixer running, add butter a few pieces at a time, beating to blend between additions. Season with a pinch of salt, if desired (I didn't add any additional salt to my frosting since I used salted butter). The frosting will be much softer and less set-up than a traditional buttercream made with butter and powdered sugar. If it seems overly runny, refrigerate the frosting for an hour or so to help it firm up - but keep in mind that this isn't a frosting to pipe with, it is meant to be soft and creamy. It has the finished texture of cream whipped to soft peaks.
  5. Run a thin knife around the cake pan to release the cake. Invert the cake onto a serving plate. Spread the peanut butter buttercream over top. Garnish with chopped chocolate and peanuts. The cake can be made and frosted up to 1 day ahead of time. Store airtight at room temperature.

Recipe Source: adapted from Bon Appetit

24 Responses to Chocolate Peanut Butter Fun Cake

  1. Amy says:

    Thoughts on doubling this and baking it in a 9×13? (I would frost it in the pan.)

    • Mel says:

      Doubling would make a really thick cake but it would probably work…you could maybe 1 1/2 it for a 9X13? Just guessing since I haven’t tried it.

  2. Heidi H says:

    Just finished eating this cake all gone! I made two cakes, in 8-in round pans, for a stacked birthday cake. I put the (truly amazing and perfect and delicious) peanut butter frosting in the middle and it turned out fantastic!! (Frosted the whole cake with vanilla buttercream then covered with MM fondant.) The peanut butter frosting was a bit oozy, so I should have done a dam of frosting. Any cake pro would have already known that…and I just learned it! Anyway, 5-star rating from me!! 🙂

  3. Cindy says:

    I made this frosting to put on top of your chocolate cupcakes perfected. A couple things I did different was use brown sugar instead of white sugar and added the peanut butter in after the butter had been incorporated. Holy Moly! Satin, buttery, heaven. I used a large round tip to pipe on top of cupcakes, drizzled with melted chocolate, then topped with chopped Reeses. They were a crowd pleaser!

  4. Jessica says:

    This cake is delicious! I was trying to find a dairy free cake for my sister’s birthday and decided to give this a try. (I always know I can count on your recipes!) Since it’s Halloween time I had some Reese’s in the house and chopped some up as the topping. The cake was nice and fudgy and the frosting… WOW! WOW! WOW! My brother declared it the best cake he’s ever eaten and I would probably say the same! Thank you!

  5. Bliss says:

    Amazing! First time in a while I’ve had dessert before dinner!

  6. I have a chocolate cake with peanut butter frosting (a classic buttercream version) that we love, but I am going have to try this frosting method next time.

  7. […] from Mel’s Kitchen Cafe, originally from Bon […]

  8. I am going to make this very soon. I might make it a bit healthier 🙂 and will let you know how it turns out. Thanks for commenting on my site and I hope you like the crispy bars :-). Beatiful family you have there!

  9. Maria says:

    I made the Bon Appetit version and I wasn’t impressed. I look forward to making the pb icing with your chocolate cake!

  10. Sarah says:

    I fixed this cake for a family gathering. There was not a crumb left in the pan. I have never gotten so many complements on a dessert before. Thank you so much for all the hard work you do for this site. I have loved all of the recipies you have posted.

  11. I can say, I’m stuck in your website. So many pretty pictures to seee *_*

  12. Deborah says:

    Looks fun – and amazingly delicious! – to me!

  13. grace says:

    ive never had peanut butter swiss meringue buttercream–ooh la la! and i like the name of this cake. 🙂

  14. Debra Kapellakis says:


  15. Sue T says:

    Hahaha Mel you crack me up. You ARE fun. And thats why I love getting your posts every day. Congrats on the new precious one!

  16. Charlotte Moore says:

    Why would you need butter in this??? it is hard for me to picture this type frosting with butter. Curious!!!

  17. Lauren says:

    My husband would LOVE this!!!!! Can’t wait to try it!

  18. Kristina says:

    Ooo I saw this recipe in Bon Appetit and I’ve been DYING to try it! Your cake looks awesome! I can never resist pb and chocolate 🙂 This looks too good!

  19. This looks amazing!!! Thanks for sharing 😀

  20. Wow, looks fun for sure! 😉

  21. I love how easy this is! Looks so yummy 🙂

  22. Kim in MD says:

    You had me at chocolate & peanut butter- my favorite dessert combination! This looks crazy delicious, Mel. I know I will have fun eating it! 🙂

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