The “Peanut Butter Cup” Cake

I make a lot of cake. My obsession with cake started over twenty years ago when I was in my early teens. Quite honestly I think cake has always been a fascination to me. Even before I got into it my mom made cakes for special occasions all the time and I can still remember sitting and watching her meticulously decorate some of these elaborate cakes. However, even with years of making cakes there was a common flaw. The cake, the texture, the flavor… in essence the “taste” and even with there almost always being a short coming I persisted. Then in this last year I went crazy making cakes. I made cakes of all sorts of flavors but it wasn’t until recently I discovered a secret that would change everything. Then it was as if the stars alined with technique, tricks, recipes, and ideas. Together they formed maybe the most perfect cake to date. The “Peanut Butter Cup” cake. 

When you google Peanut Butter Cup Cake there is one thing you’ll see they all have in common; they all have a chocolate cake and a peanut butter filling. To me this is all wrong. When you bite in to a Reese’s Peanut Butter Cup there is a great ratio of peanut butter to chocolate. I am sure all those cakes are delicious in their own way but it wasn’t what I was looking for.

This cake started with a revelation. GMS. This is the secret ingredient that anyone who loves to make cakes from scratch needs to know about. What is GMS?? It’s Glycerol Monostearate. This is an emulsifier the helps hot fat and water together on a chemical level. This is important in cakes because it will allow you to have lots of tiny bubbles in your batter as it bakes and in turn allows you to have a moist cake with a great crumb! So where did I hear about this wonder product? Chefsteps.com! They have tons of great cooking tips and an entire master class on cake baking.

Taking what I learned from that I wanted to experiment with making my own flavors of cakes. The issues start to arise when you start swapping ingredients you want to make sure you’re swapping like for like. You can still have issues with how the different ingredients interact. They might have more liquid, they might have different pH, they might add too much salt, and so on but that’s what experimentation is all about.

The next  and MAJOR step in this cakes evolution was when I purchased a copy of Stella Parks new cookbook Bravetart. The very first recipe I picked to make from her book was the one I have had the most problems with; the peanut butter cookie. Often this cookie comes out hard and, in my opinion, not sweet enough. It was the first step that caught my attention. It was making Honey-Roasted Peanut Flour. Now, anyone who loves to bake probably already knows about nut flours and how great they can be but good luck finding niche nut flours like honey-roasted peanut flour. What’s great is Stella makes this so simple! Take all-purpose flour and put it in a food processor add the desired nut and pulse until all the contents are the same texture. Presto! Honey-Roasted Peanut Flour! I have to tell you the smell is AMAZING! Oh, and if you were wondering the cookies turned out amazing!

Armed with Honey-Roasted Peanut Flour as a technique I knew what I had to try. A peanut cake! And if you’re going to make a peanut cake there is only one sensible option to frosting, chocolate. So, as I dug through Stella’s cookbook I came across her recipe for White Cake. This struck me as a great canvas to manipulate into my idea of a peanut cake. As I was debating about how much peanut to swap in place of flour I discovered that at the end of the recipe she offered a guide for adding hazelnuts. This eliminated the guess work and all I had to do was use peanuts instead of hazelnuts.

Now it was time to merge everything I had learned from my Chefsteps Master Class and Bravetart’s recipe for the “nut” cake. This took a lot of swapping of ideas and techniques. first and foremost was adding the peanuts to the flour. Next, I knew I wanted to use roasted peanut oil as the bulk of the fat for this cake. I took the total of the coconut oil and butter and divided it in half, making have my fat the peanut oil and half the butter. This was to help round out the peanut flavor in the cake its self. The next part was the hardest… trying to figure out how much GMS to use in my cake. Neither, Chefsteps.com or Modernistpantry.com, offered a ratio for use in any cake recipe. What’s great though is that Chefsteps, Modernist Pantry, and Bravetart are all fantastic at responding to questions on Twitter. So I tweeted all of them and through a few back and forth’s we came to the conclusion that 2% of the weight of the flour being used was the way to go. My final alteration was the milk. In the White Cake recipe it calls for all buttermilk. However, one of the helpful tips in my masterclass was to add some of the liquid at the very end warmed. This lead me to use both milk and buttermilk, adding the warmed milk at the end.

So to recap I took what I am sure is a fantastic recipe to begin with and changed the flour, the fat, the milk and added a new chemical component. If that’s not experimenting I don’t know what is! I put my cake in the oven and waited. It baked for nearly 45 minutes. When it finally hit 205ºF (another tip I learned from Chefsteps and also is called out in Bravetart, although she recommends 210ºF) I took the cake out of the oven. OMG the smell was heavenly. This sweet honey and peanut smell wafting through the kitchen. It took everything in us for my husband and I not to just eat the cake!

Now I needed to come up with a delicious peanut filling and a chocolate icing. The peanut filling I finally settled on was one from The Dahlia Bakery Cookbook. In it they had a Peanut Butter Sandwich Cookie and I remembered filling was easy and delicious.  However, before I could make fillings I needed to make my Chocolate icing. In Bravetart she had a few and I finally settled on the Marshmallow Buttercream with the Dark Chocolate variation she offers up in the “mix it up” section following the recipe. I should say that I have been a recent convert to Italian Buttercream, so when I read about her marshmallow buttercream I was curious enough to try. When I set out to make the frosting my husband was helping me in the kitchen. Since I joke he’s the science guy of the household I put him on the last of making the marshmallow cream. It took some doing but we ended up with a bowl of white goo. Somewhere along the way in making it something went wrong. Once it set up it was more like the beginnings of taffy than marshmallow. Trying to trust the recipe I dumped it into my kitchen aid with the whisk attachment and started it up to be able to start adding butter. They marshmallow was so tough it started to bend my whisk attachment! I had been able to add butter and as I did it started to get fluffy and more like frosting but there were all sorts of complications.

I jumped on Twitter and shot Bravetart a question about what might have gone wrong. Stella was amazing! She and I must have been going back and forth for a while. In the end I think the issue was two-fold. One I think the mixture was over cooked because it took nearly twice as long as the recipe said it would to hit the target temperature and secondly my mixer I was using to whip it was an older kitchen aid that just didn’t seem to have the oomph to get air into the mixture.

With a lot of creative trouble shooting we finally ended up with something the resembled frosting. Now it was time to add the chocolate. I started with a lower amount of chocolate but just wasn’t getting the color I wanted so I kept adding more. I think in the end I mist have added about 12-14 ounces of chocolate to the frosting and it was still looking more “milk” chocolate than “dark”. The biggest issue was that adding all this melted chocolate cause my frosting to get too soft. I ended up putting the whole thing into the fridge, let it get pretty firm and whipped it again. At that point I finally had a good consistency for frosting.

The peanut butter filling went without incident but wasn’t as fluffy as I thought I remembered it being. At this point I was just determined to get the cake assembled. I piped a “flood” boarder on the first layer and filled it in with my peanut butter filling. I then layered on the next cake and repeated the process. I then iced the whole thing in chocolate frosting. The top had more of a marbled effect because my peanut butter filling hadn’t fully set up. I called it done and put the cake into the fridge. It still made me a little sad that it didn’t have that hard candy looking shell of a peanut butter cup but I tried to just move on. The next morning I decided I was going to make a dark chocolate ganache and poor it over the whole thing. Thankfully Bravetart had a recipe for that as well which was simple and straightforward. I made my ganache let it cool a little and then poured it over the cake spreading it out to make a nice solid coat. Now I had the look I imagined!

I can’t even tell you with all the ups and downs of trying to get this cake to the eating point, when I finally cut into it the anticipation was high! Oh, boy, did it deliver. It looks like a peanut butter cup with a center of pure golden peanut goodness and hit all the right notes. The cake was moist and a perfect crumb. This is now a permanent cake in my arsenal. The thing I learned from this experience is to trust me instincts when it comes to concepts and flavors, when in doubt ask the pros, and in the end it’s just cake.

One last tip, cake should ALWAYS be served at room temperature. I pull the servings of cake out of the fridge, put them on plates, cover them with plastic wrap, and then come time after dinner they are the perfect temperature.

Peanut Butter Cup Cake

“Peanut Butter Cup” Cake 

FOR THE CAKE:

  • 12 ounces bleached cake flour
  • 9 ounces Honey Roasted Peanuts
  • 16 ounces Granulated Sugar
  • 9.5 grams baking powder
  • 5.8 grams baking soda
  • 2.9 grams kosher salt
  • 11.9 grams Glycerol Monostearate
  • 6 ounces Peanut Oil
  • 6 ounces Unsalted Butter, room temperature
  • 8½ ounces egg whites, room temperature
  • 1 ounce vanilla extract
  • 1 teaspoon Almond Extract
  • 8 ounces Buttermilk
  • 8 ounces Whole Milk, warmed

FOR THE FILLING:

  • 14 ounces Creamy Peanut Butter, preferably Skippy
  • 3 ounces Unsalted Butter
  • 4 tablespoons Powdered Sugar
  • 2 tablespoons Honey
  • 1 teaspoon Salt

FOR THE MARSHMALLOW BUTTERCREAM:

  • 1 envelope (¼ ounce) Unflavored Gelatin Powder
  • 2 ounces Cool tap Water
  • 1 tablespoon Vanilla Extract
  • 6 ounces Water for the Sugar Syrup
  • 10 ounces Light Corn Syrup
  • 14 ½ ounces Granulated Sugar
  • ½ teaspoon Salt
  • 20 ounces Unsalted Butter
  • 12 ounces 70% Chocolate, chopped

FOR THE GANACHE:

  • 8 ouches Heavy Whipping Cream
  • 8 ounces 66% Chocolate, chopped

FOR THE CAKE:

  1. Preheat your oven to 300ºF. Prepare two 9-inch square pans by spraying with a non stick spray and line the bottom with parchment.
  2. In the bowl of a food processor add the flour and the peanuts. Pulse until the mix is a fine peanut flour.
  3. In a large bowl add the peanut flour, sugar, salt, baking soda, baking powder, and glycerol monostearate. Whisk together to fully combine.
  4. In the bowl of a stand mixer add the oil, butter, egg whites, vanilla, almond extract, and buttermilk. Fitted with the paddle attachment beat on low until you get a homogenous liquid.
  5. With the mixer still running add the dry mixture a extra large spoonful at a time until all the dry mixture is added. Add the warmed milk to the mixture in a slow steady stream. Stop, remove the bowl, scrape down the sides and divide between two 9-inch square pans.
  6. Bake for 40-50 minutes, until a instant read thermometer registers 205ºF. Let cakes fully cool in their pans before turning them out.

FOR THE FILLING:

  1. Put all the ingredients into a bowl of an electric mixer fitted with a whisk attachment and beat until fluffy. Set aside until ready to use.

FOR THE MARSHMALLOW BUTTERCREAM:

  1. In a small bowl mix the gelatin, cool water, and vanilla and set aside. In a medium sauce pan add the 6 ounces of water, corn syrup, sugar, and salt. Set the pot over medium to medium high heat. Attach a candy thermometer and heat the sugar mixture to 250ºF. This should take about 8 minutes.
  2. Remove the thermometer, attach it to the bowl of your stand mixer and pour in the hot sugar mixture. Allow it to cool to 212ºF then add the gelatin. Mix on low until the tow mixtures are fully incorporated, then raise the speed to medium high and whisk until the marshmallow has tripled in volume, about 10 minutes.
  3. Transfer the marshmallow base into a well greased stainless steel bowl. Let it sit for 2 hours to fully set up. Once the marshmallow base is set transfer it to the bowl of your stand mixer fitted with the whisk attachment. On medium low speed start adding the butter one dollop at a time before adding the next one. As the marshmallow begins to fluff raised the speed and continue to beat until all the butter is incorporated.
  4. Melt the chopped chocolate. Let it slightly cool and add to the buttercream. If your buttercream becomes too “loose” pop the bowl, whisk and all into the fridge and let it cool then whisk again.

FOR THE GANACHE:

  1. Pour the cream into a small sauce pan and bring to a simmer. Remove from the heat and add the chocolate. Whisk until smooth. Pour into a clear measure with a handle and a spout. Let it cool slightly and then use immediately.

ASSEMBLED THE CAKE:

Place one peanut cake on your desired board or platter. Pipe a “flood” boarder with the chocolate icing. Fill with the peanut butter filling, set the top layer of cake on top, and repeat the “flood” boarder and peanut filling. Ice the sides with the chocolate frosting and smooth out the top. Put the cake in the fridge and let it set up over night. The next day make your ganache, let it cool slightly, and pour over the cake, smoothing out as you pour, to create a “hard candy finish”.

10 thoughts on “The “Peanut Butter Cup” Cake

    • In Stella Parks cookbook Bravetart she talks about the origins of the marshmallow buttercream and how she modernized it a little. The benefit of the marshmallow is you can add flavors even things like fruit puree’s and it will hold up better than traditional buttercream because of the gelatin. You should check out her book.

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  1. Right now, I’m w/o a stove-oven. (Tree hit my house, lost all appliances and dependent upon a micro/toaster oven and hot plate.) This is going to be the first thing I bake when the new range arrives mid-October. CAN’T WAIT!!!!!!!!!!!!!

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    • So sorry about your house! Glad you’re safe. I have big trees all around my house it’s my biggest fear. As you are aware, I’m sure, baking can be very therapeutic so baking this cake might help once you get you’re appliances! Enjoy!

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