The combination of rich cocoa and fluffy peanut butter frosting makes this Chocolate Peanut Butter Slab Cake a true indulgence for any sweet tooth. Made for feeding a crowd, this cake delivers on flavor and show-stopping presentation, without the fuss of layer cakes.
Perfect for parties, potlucks, and birthdays, it’s loaded with crunchy peanuts, luscious drizzle, and mini Reese’s cups. It’s a crowd-pleaser that doesn’t just look stunning—it tastes like pure happiness. Each slice packs a punch of chocolatey richness and creamy peanut butter goodness, making it one of those desserts people will request again and again.
Full Recipe:
For the Cake:
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1 3/4 cups all-purpose flour
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3/4 cup unsweetened cocoa powder
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1 1/2 tsp baking powder
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1 1/2 tsp baking soda
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2 cups white sugar
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1 tsp kosher salt
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2 large eggs
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1 cup milk (low or full-fat)
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1/2 cup vegetable oil
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2 tsp vanilla extract
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2 tsp instant coffee powder (optional, enhances chocolate)
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1 cup boiling water
Peanut Butter Buttercream Frosting:
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250g unsalted butter, softened
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4 cups (500g) powdered sugar, sifted
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1/2 cup smooth peanut butter (spread-style)
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1/4 tsp kosher salt
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1 tbsp milk
Optional Toppings:
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1/2 cup chocolate chips or melts
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2 tbsp heavy cream
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3 tbsp peanut butter (melted for drizzle)
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120g mini Reese’s Peanut Butter Cups (whole and halved)
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1/4 cup salted peanuts, finely chopped
Directions:
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Preheat oven to 350°F (180°C). Grease and line a 9×13″ metal pan with parchment paper.
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In a large bowl, sift together flour, cocoa powder, baking powder, and baking soda. Add sugar and salt. Whisk to combine.
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Add eggs, milk, oil, and vanilla. Whisk until smooth.
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Dissolve coffee powder in boiling water. Pour into the batter and whisk well. Batter will be thin.
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Pour into prepared pan. Bake for 45 minutes or until a skewer inserted comes out clean. Cool completely (~2 hours).
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For frosting: Beat butter until fluffy (3 min). Add powdered sugar in thirds, beating after each addition. Add peanut butter, salt, and milk. Beat for 3 more minutes.
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Spread frosting over cooled cake.
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Melt chocolate chips with cream in microwave (15 sec bursts). Cool 10 mins. Drizzle over cake with melted peanut butter.
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Scatter peanut butter cups and chopped peanuts over top. Drizzle remaining chocolate and peanut butter.
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Slice and serve. Store in fridge, but bring to room temp before serving.
Prep Time: 30 minutes | Cooking Time: 45 minutes | Total Time: 3 hrs 15 minutes
Kcal: 395 kcal | Servings: 25 servings
A Celebration-Worthy Dessert for Every Occasion
This Chocolate Peanut Butter Slab Cake isn’t just any dessert—it’s a show-stopping centerpiece designed for celebrations, parties, or any gathering where you want to wow a crowd. Whether you’re baking for a birthday, a potluck, or just to satisfy a group of sweet tooths, this cake delivers indulgent flavor and irresistible appeal. What sets it apart is not just the iconic flavor combo of chocolate and peanut butter, but also its practicality and ease of preparation. Unlike multi-layered cakes that can be tricky to bake, stack, and slice, this slab cake format is a straightforward solution that’s big on flavor and perfect for slicing into tidy, generous portions.
The Magic Behind the Slab Cake Format
Slab cakes are a game-changer for home bakers who want impact without stress. This recipe ditches the traditional towering layer cake in favor of a single-layer rectangular beauty. The format makes decorating, slicing, and transporting a breeze. It also offers more surface area for generous toppings like peanut butter cups, chocolate drizzle, and chopped peanuts, turning the cake into an edible canvas. The single-layer build avoids the common issues of uneven stacking, collapsing layers, or frosting meltdowns. It’s less about fuss and more about fun and flavor.
Another benefit? A higher cake-to-frosting ratio per bite. For many, this balance is what makes each mouthful truly satisfying. And from a serving perspective, the rectangular shape makes it simple to cut evenly into up to 25 portions, which is ideal for sharing.
A Cake That Starts With Simplicity
Despite its gourmet look, this cake is rooted in simplicity. The batter comes together in a single bowl—no fancy mixers or techniques required. It’s an oil-based cake, which gives it an incredibly moist texture and excellent shelf life. Oil remains liquid at cooler temperatures, unlike butter, which firms up. This means the cake stays soft even when refrigerated. Additionally, the recipe calls for boiling water and optional coffee granules, which help “bloom” the cocoa powder and enhance the depth of the chocolate flavor. The end result is a rich, velvety cake that holds together well without being dense.
The Fluffy, Dreamy Peanut Butter Frosting
One of the standout features of this cake is the peanut butter buttercream. It’s whipped until light and airy, then generously spread over the chocolate base. Using standard peanut butter spread (not natural peanut butter) ensures the frosting holds its shape while delivering that iconic sweet-salty peanut flavor. A pinch of salt cuts through the sweetness, adding a layer of complexity that makes each bite sing. The texture is so creamy that it glides across the cake smoothly, making even a casual swirl look effortlessly beautiful.
Going Over the Top—Literally—with Toppings
This cake’s aesthetic is what some might call a “controlled chaos”—a deliberate splash of toppings that resemble a Jackson Pollock painting, only better because it’s edible. The peanut butter cups, both whole and chopped, bring that instant visual recognition factor. Meanwhile, melted chocolate and runny peanut butter are drizzled generously, adding a decadent final touch. Chopped salted peanuts are scattered across the top, offering crunch and a hint of savoriness that complements the sweetness.
These toppings aren’t just for looks—they add contrast in texture and flavor. You’ve got the creamy frosting, the moist cake, the dense chew of peanut butter cups, and the crunch of peanuts. Every bite is an adventure, and no two pieces are exactly the same.
Feeds a Crowd Without Compromise
One of the most practical aspects of this cake is how well it serves a large group. Because of its rich flavors and generous toppings, you don’t need massive slices to feel satisfied. It comfortably serves 20–25 people, making it an ideal choice for office events, large family gatherings, bake sales, or birthday parties. It’s easy to portion, doesn’t require refrigeration during a party, and holds its structure well even after several hours at room temperature.
Plus, if you’re planning ahead, this cake keeps beautifully in the fridge for up to five days. Just bring it to room temperature before serving to soften the frosting and restore that dreamy texture.
Adaptability for Dietary Needs and Preferences
While the standard recipe uses traditional ingredients like flour, eggs, and dairy, many home bakers have successfully adapted this cake to suit various dietary needs. Substituting the milk for non-dairy alternatives like oat, soy, or almond milk works well, and oil-based cakes tend to be more forgiving to ingredient swaps. Vegan adaptations can be achieved by replacing eggs with banana, flaxseed, or commercial egg replacers. And if you need to make it gluten-free, a 1:1 gluten-free flour blend can usually be substituted with little effect on the final texture.
Although the original version is indulgent, you can always reduce the sweetness slightly or scale back on toppings to suit your personal taste.
Kid-Friendly, Party-Ready, and Always Crowd-Pleasing
What makes this cake truly stand out is how universally loved it is. Kids are drawn to the familiar peanut butter cup topping, while adults appreciate the rich, well-balanced flavor. Its presentation is casual enough for a backyard BBQ and polished enough for a dinner party. It’s also highly interactive for group baking—perfect for letting kids help decorate or for creating a DIY topping station where guests can add their own final flourishes.
If you’re into gift baking or want to bring something special to a gathering, this cake makes a great impression. Plus, it travels well and doesn’t require refrigeration for short trips.
Visual Appeal Without the Pressure
There’s a reason this cake is often described as “outrageous”—its look is bold, unpretentious, and absolutely Instagram-worthy. The layered drizzles, the random (but somehow artful) scatter of peanut butter cups, and the glossy shine from melted chocolate and peanut butter create an image that’s as inviting as it is mouthwatering.
But what’s even better is how forgiving the decorating process is. You don’t need to be a skilled cake decorator to pull this off. In fact, the more organic and relaxed the topping placement, the better the final effect. It invites creativity and takes the pressure off—ideal for bakers who want a big impact with minimal stress.
Behind the Recipe: A Celebration in Itself
This recipe was originally created to celebrate a milestone—the release of a new cookbook—and it embodies the same warmth, passion, and practicality that defines great home cooking. It’s about celebrating big flavors and joyful occasions, without needing professional kitchen tools or techniques.
The story behind the cake reflects the real-life journey of balancing ambition, personal challenges, and community. It’s a reminder that great food can come from humble beginnings, and that baking can be both therapeutic and rewarding.
Conclusion: A Cake That Delivers on Every Level
In the world of crowd-pleasing desserts, the Chocolate Peanut Butter Slab Cake stands out as a masterpiece of flavor, ease, and fun. From its rich, moist chocolate base to its fluffy peanut butter frosting and outrageous toppings, it hits every note perfectly. It’s designed to impress without intimidation, making it ideal for both seasoned bakers and enthusiastic beginners.
Whether you’re baking it for a birthday bash, a workplace celebration, or simply because you deserve something sweet, this cake promises joy in every bite. With its stunning presentation, satisfying texture, and unbeatable taste, it’s more than just a dessert—it’s an experience worth sharing.