Chocolate & Peanut Butter Bar Cake is the dessert I reach for when I want a rich, bakery‑style chocolate cake layered with thick ribbons of creamy peanut butter. It starts with a deeply chocolatey sponge made from cocoa, flour, and sugar, then stacks up with smooth peanut butter frosting between each layer and a glossy chocolate finish on top. Every bite hits that perfect balance of fudgy chocolate and salty‑sweet peanut butter that fans of this combo love.
This style of cake bakes up moist and tender thanks to a thin batter enriched with oil, milk, and boiling water, similar to classic chocolate peanut butter layer cakes. The “bar cake” look comes from building tall, even layers and slicing generous rectangular slabs instead of wedges, which shows off the stripes of cake, filling, and any contrasting layers or toppings you add.
Ingredients for Chocolate & Peanut Butter Bar Cake
For the chocolate cake base (using your dry ingredients as the core):
- 1 3/4 cups all‑purpose flour
- 1 1/2 cups granulated sugar
- 3/4 cup unsweetened cocoa powder
- 1 1/2 teaspoons baking powder
- 1 1/2 teaspoons baking soda
- 1 teaspoon salt
- 2 large eggs
- 1 cup milk or buttermilk
- 1/2 cup vegetable oil
- 2 teaspoons vanilla extract
- 1 cup boiling water or hot coffee for extra depth
For the peanut butter filling/frosting:
- 1 cup creamy peanut butter
- 1/2 cup unsalted butter, softened
- 2–3 cups powdered sugar
- 1–4 tablespoons milk or cream, as needed
- Pinch of salt and a splash of vanilla extract
For chocolate glaze or ganache topping (optional but great for a glossy finish):
- 1/2 cup heavy cream
- 4 ounces dark or semisweet chocolate, finely chopped
- 1 tablespoon butter for shine (optional)
Garnish ideas: chopped chocolate, peanut butter cups, nuts, or fresh berries for contrast.
How I Make Chocolate & Peanut Butter Bar Cake
1. Prepare pans and oven
I preheat the oven to 350°F (175°C). Then I grease and line two or three 8‑inch square or round cake pans with parchment. Using square pans helps later when cutting bar‑style slices, but round works too—you can trim edges if you want clean bars.
2. Mix the chocolate cake batter
In a large bowl, I whisk together flour, sugar, cocoa powder, baking powder, baking soda, and salt until well combined. I add the eggs, milk, oil, and vanilla, then beat on medium speed for about 2 minutes until the mixture is smooth. Finally, I pour in the boiling water or hot coffee and mix on low until the batter is thin and glossy. It will seem runny, but this is what creates an extra‑moist cake.
I divide the batter evenly among the prepared pans and bake for about 25–30 minutes, or until a toothpick inserted in the center comes out with just a few moist crumbs. I let the cakes cool in the pans for 10 minutes, then turn them out onto racks to cool completely.
3. Make the peanut butter frosting
For the filling, I beat the softened butter and peanut butter together until creamy and smooth. I gradually add the powdered sugar along with a pinch of salt and a bit of vanilla, mixing until thick and fluffy. If it’s too stiff, I splash in milk or cream a tablespoon at a time until it’s spreadable but still holds its shape between layers. This gives a rich, truffle‑like peanut butter stripe in the finished bar cake.
4. Stack the bar cake
Once the cake layers are completely cool, I level their tops if needed. For a tall bar‑style dessert, I often cut each cake layer in half horizontally so I have four thin chocolate layers. I place the first layer on a board, spread a generous amount of peanut butter frosting all the way to the edges, then repeat with the remaining layers to create alternating stripes of chocolate and peanut butter. A thin crumb coat on the outside keeps crumbs locked in, or I leave the sides mostly exposed for a “naked” layered look.
5. Add the chocolate glaze
To make ganache, I warm the cream just to steaming, pour it over the chopped chocolate, let it sit for a few minutes, then whisk until smooth and glossy. A little butter stirred in at the end adds shine. I let it cool to a pourable but slightly thick consistency, then pour it over the chilled cake, smoothing it gently so it forms a sleek top without running too far down the sides—perfect for that polished bar‑cake finish.
I garnish the top with chopped chocolate, crushed peanut butter candies, or berries and chill the cake until the ganache sets.
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