Chocolate Peanut Butter O.M.G. Cake

This cake is not for the faint of heart. It’s a rich, dark chocolate cake layered with peanut butter frosting, crushed Oreos, and dark chocolate peanut butter ganache.

The story

Yes, O.M.G. is both an odd and possibly pretentious name for a cake. But I didn’t name it! This cake is named after my favorite flavor at an ice cream shop in our town. It’s chocolate peanut butter ice cream with these peanut butter filled Oreos that just make my life so happy. It’s a rich, fairly sweet ice cream.

It just so happens to be my dear friend’s favorite flavor, too. So, for her birthday, I decided to create a cake version of our beloved O.M.G. ice cream.

This cake is my Chocolate Charity Cake taken up a notch. I did some research and experimenting and found that melting chocolate chunks in the hot coffee of my original recipe did the trick in creating a super rich, very fluffy cake.

Tips for this dessert

Do NOT overbake

You’ll want to watch this cake closely as it gets toward the end of the bake. I baked mine for somewhere between 22 and 25 minutes and it was about 1-2 minutes overdone. Still delicious, but the edges had the faintest hint of drying out.

If you’re using 2 cake pans, that’s fine, just increase the bake time and be cautious toward the end—as soon as you have no wet batter on your toothpick (or kebab stick, like me…) you’re done!

Finally, only cool in the pans for about 5 minutes then turn onto a wire rack or plate. I usually skip this step, but it’s helpful in maintaining a moist cake here.

Divide into 2 pans if you want more filling

I wrote the recipe for the cake I photographed (3 layers), but honestly I prefer doing 2 pans, cutting each cake in half, and having an extra layer of filling. However, the recipe as-is requires less work and is still yummy!

Make your own buttermilk

In this recipe, I found that making my own buttermilk (which I was forced to do because Trader Joe’s was out of buttermilk and I had no time to visit another store) helped it rise perfectly. My most recent baking education taught me the value of an acid (such as the vinegar in homemade buttermilk) to work with baking soda, and I believe my unintentional use of it actually helped. This was a moist, fluffy, yet sturdy cake.

However, if you have buttermilk you’d like to use up or just prefer it, it will work just as well. It’ll make the cake slightly more moist but also at risk of cracking, so handle with care.

Soften your butter for 1 hour max

I read a lot of recipes and baking tips, and one I’ve been seeing a lot of lately is to only leave your butter out for an hour. Longer can lead to slightly melty butter that won’t whip up all nice and fluffy and may cause your frosting to break or curdle or just slide right off the cake. Yep, I’ve had all of those happen.

If your butter does get too soft—where you can press your finger into it with no resistance at all and it’s kinda glossy/greasy—throw it back in the fridge or freezer for a few minutes until you can easily make a small indentation. A good rule of thumb is to not let it get that shiny look that about-to-melt butter gets.

I strongly caution against “softening” in a microwave. It can’t evenly soften and usually causes the inside of the butter to melt slightly.

Honestly, in a pinch you can get away with whipping cold butter with the paddle attachment for about a minute until it’s smooth. Most American buttercreams and standard variations (like this peanut butter version) will work just fine if you do this, as the beating process tends to bring it to room temperature. If you’re baking in a very warm house, this could be a good alternative.

Use Oreo Thins if you want that cookie crunch

Layering cookie pieces in a cake often results in soft, sometimes soggy cookies. Oreo Thins are thinner (obvs) and thus crunchier and less likely to get soggy. However, regular Oreos may be the texture you want. This recipe has a nice crunch to it, so if you don’t like that, regular Oreos will do just fine.

Stir the ganache constantly until smooth

The various fats in this ganache make for a finicky mixture. You don’t want it separating or seizing up (when the chocolate hardens and is unsalvageable).

The same actually goes for the coffee “ganache” that goes in the cake. Stir well and nonstop until the chocolate melts smoothly. If you have some granules left in the bowl, use a mesh sieve to strain those out.

Use unsweetened peanut butter, unless you want a very sweet cake

Because you need a decent amount of powdered sugar to stiffen your frosting so it doesn’t slide off your cake like a popsicle in July, you don’t want hidden sugar already in your ingredients. I used natural peanut butter, the kind you have to stir when you open it. This is why the chocolate peanut butter ganache almost separated, so you can use something like unsweetened Jiff or Skippy or the like if you’re not comfortable working with finicky ingredients.

The peanut butter ratio is flexible

If you want a lighter peanut butter taste, replace it in the frosting with butter and simply cut back on it in the ganache (no replacements).

If you want an even more peanut buttery taste, you can increase it to a point. In the ganache, you’ll need a little more heavy cream (unless you’re not working with natural peanut butter, in which case you should be fine). In the frosting it gets trickier. The recipe I’m sharing is the original ratio I used that created a perfectly peanut buttery, slightly sweet, smooth frosting. But I was worried I didn’t have enough (I did 🤦‍♀️) so I tried increasing it one ingredient at a time. At one point my frosting seemed dry, partly because of the natural peanut butter I used and partly because I added too much peanut butter in my foolish venture to increase the amount of frosting.

So, if you increase the peanut butter in the frosting, you can reduce the butter by the same amount or try increasing the powdered sugar. But I make no promises as to the smoothness or frost-ability of that frosting, since my experience was precarious.

Chocolate Peanut Butter “O.M.G.” Cake

• prep time: 60 minutes
• cook time: 25 minutes
• total time: 1 hour 25 minutes, plus assembly time (note: I usually make frosting, fillings, etc. while the cake bakes, which cuts my working time to about an hour before I assemble the cake)

Servings: 12-15

Ingredients:

For the dark chocolate cake:

• 1 tablespoon white vinegar plus enough whole milk to equal 1 cup of milk/vinegar mixture
• 1 cup fresh, strong coffee
• 3 ounces semisweet or dark chocolate (chips, chunks or baking bar all work fine)
• 1 2/3 cup all purpose flour
• 1 1/2 cup sugar
• 3/4 cup unsweetened cocoa powder (Dutch process will make a richer chocolate taste, and you can add up to 2 tablespoons for a death-by-chocolate taste)
• 1 1/4 teaspoons baking powder
• 1 teaspoon baking soda
• 1/2 teaspoon sea salt (or 1 teaspoon table salt)
• 2 eggs, room temperature
• 1/2 cup avocado or olive oil
• 1 tablespoon pure vanilla extract

For the peanut butter frosting:

• 1 cup (2 sticks) unsalted European style butter, softened for 1 hour
• 1/2 cup unsweetened peanut butter (stir well if using natural)
• 3-4 cups powdered sugar
• 1/4 teaspoon sea salt (or to taste)
• 2-4 tablespoons heavy cream or milk
• 1 teaspoon pure vanilla extract (optional, adds a softer, creamier flavor)

For the chocolate peanut butter ganache:

• 2 ounces semisweet chocolate (weighed, not measured by volume)
• 2-4 tablespoons peanut butter, to taste
• 1/3-1/2 cup heavy cream (start with 1/3 then increase if, as it all melts, it’s getting too thick)

To decorate:

• 1 row (1/2 package) Oreo Thins, filling removed (or regular Oreos or similar chocolate wafer cookie)

Instructions:

For the cake:

1. Prep the homemade buttermilk. Add 1 tablespoon white vinegar to a liquid measuring cup. Then fill to the 1 cup line with whole milk (if using less than whole, add a few splashes of heavy cream to increase the fat content). Let stand for about 30-60 minutes to create buttermilk and to bring to room temperature. See note above about using regular buttermilk.
2. Once buttermilk is ready, preheat oven to 350 (325 if using convection). Grease three (or two, see note above) 8” round pans with baking spray or butter and flour. Line with parchment paper.
3. Prep the coffee ganache. Add 1-2 inches of water to a small saucepan, bring to a boil then reduce heat to medium low (or whatever temp keeps a good simmer going on your stove). Combine the coffee and chocolate in a small glass, heatproof bowl (or the bowl of a double boiler, props if you actually own one). Set over the pan of simmering water and stir constantly with a rubber spatula until all of the chocolate melts. Set aside (but don’t make ahead, you want it warm when you add it to the cake).
4. In the bowl of a stand mixer (or a large bowl) whisk together the flour, sugar, cocoa powder, baking soda, baking powder, and salt until evenly distributed. You’ll know this is the case when it’s evenly cocoa-y.
5. In a separate bowl, whisk together the buttermilk, eggs, oil, and vanilla until very lightly frothy. Slowly—SLOWLY—whisk in the coffee/chocolate mixture while whisking quickly and constantly. Once you’ve added a little more than half the coffee you can speed up your pour a bit, because the eggs are tempered by then.
6. With the paddle attachment of your stand mixer on the lowest setting, slowly pour the wet ingredients into the dry. Scrape the bowl, getting to the very bottom, then increase the speed to medium and mix until batter is smooth, about 1 minute. Don’t over mix.
7. Pour batter evenly between the three pans. Bake for 20-25 minutes, checking around 17 minutes with a toothpick and baking until no wet batter comes out. Cake crumbs are fine and usually a good sign. If using only two pans, increase baking time by about 10 minutes. Let cool in pans for 5 or so minutes then turn onto a wire cooling rack or plate to prevent it drying out.

For the frosting:

1. With the paddle attachment fitting to a stand mixer (or in a large mixing bowl with handheld beaters), beat the butter and peanut butter on medium until well blended and a bit fluffy (1-2 minutes), scraping bowl at least once to fully incorporate all ingredients.
2. Add powdered sugar, one cup at a time, beating until well blended and scraping bowl after each addition. Halfway through, add the salt, vanilla, and heavy cream, 1 tablespoon at a time, to smooth the frosting. The goal is to get it smooth without making it a loose, watery frosting, so it’s easier to err on the dry side and add more cream at the end than it is to recover from a loose frosting. Add powdered sugar until desired taste is reached.
3. If the frosting is too stiff, add more heavy cream 1 tablespoon at a time. If it’s too loose, add powdered sugar 1/4 cup at a time.

For the chocolate peanut butter ganache:

1. Just like the coffee “ganache” for the cake, add all ingredients to a heatproof bowl set over a pan of simmering water (or to the bowl of a double boiler). Stir with a rubber spatula until melted and smooth, scraping sides and bottom to avoid any chocolate seizing. If it is looking too thick, add a splash (or more, depending on your results) of heavy cream to thin it out. You want to be able to drizzle it on the cake, not have it fall in blobs from the spoon.

To assemble:

1. If working with 2 cakes instead of 3, cut each cake in half to make 4 layers.
2. Crumble the Oreo wafers (filling removed, no judgement if you ate it with a spoon!). Leave some pieces about the size of a pea to get a nice crunch.
3. Fill cake layers with a thin layer of frosting (roughly 1/4”). Spread 1/4 to 1/3 of the crumbled Oreos evenly on top of the frosting. Drizzle with ganache (you’ll have a little extra, so drizzle as much or as little as you’d like). Repeat until cake is complete. Add a thin crumb coat and refrigerate 10-20 minutes.
4. Add a layer of frosting on top of the crumb coat (to desired thickness). Top cake with remaining Oreos and drizzle with ganache.

Enjoy! (Probably in thin slices with a glass of milk...this is beautifully rich!)