Introduction
Chocolate and peanut butter have a legendary status as a flavor duo: rich, salty‑sweet peanut butter cuts through deep cocoa, creating a dessert that is both indulgent and perfectly balanced. A Chocolate & Peanut Butter Bar Cake leans into that combination by layering a fudgy chocolate base with a creamy peanut butter layer and a smooth chocolate topping. Baked in a rectangular pan and sliced into bars, it is easier to transport and serve than a traditional round cake yet feels just as special on a dessert table.
This style of dessert borrows ideas from brownies, peanut butter bars, and classic layer cakes. The bottom layer behaves like a dense chocolate cake or brownie; above that sits a whipped peanut butter filling inspired by frosting but slightly firmer so it holds clean slices; finally, a glossy chocolate ganache or glaze seals everything together. The result is a bar cake that slices beautifully, keeps well in the fridge, and satisfies anyone who loves that chocolate‑peanut butter pairing.
Ingredients
The recipe below makes one 9×13‑inch (23×33 cm) pan of bar cake, which can be cut into 16 large or 24 smaller pieces. You can halve everything and bake in an 8×8‑inch pan if you want a smaller batch. All ingredients are common pantry staples: cocoa, flour, butter, eggs, peanut butter, and chocolate.
For the Chocolate Cake (Base Layer)
- 1 cup (130 g) all‑purpose flour
- 1 cup (200 g) granulated sugar
- 1/3 cup (35 g) unsweetened cocoa powder
- 1 teaspoon baking powder
- 1/2 teaspoon baking soda
- 1/2 teaspoon fine salt
- 2 large eggs, at room temperature
- 1/2 cup (120 ml) buttermilk or milk mixed with 1 teaspoon vinegar
- 1/3 cup (80 ml) neutral oil (such as canola or sunflower)
- 1 teaspoon vanilla extract
- 1/2 cup (120 ml) hot water or hot coffee
For the Peanut Butter Layer
- 1 cup (240 g) creamy peanut butter (not natural stir‑type if you want a smoother set)
- 1/2 cup (115 g) unsalted butter, softened
- 2 cups (240 g) powdered sugar, sifted
- 1–3 tablespoons milk or cream, as needed
- 1 teaspoon vanilla extract
- Pinch of salt (omit if your peanut butter is very salty)
For the Chocolate Topping
- 1 1/2 cups (255 g) semi‑sweet chocolate chips or finely chopped chocolate
- 3/4 cup (180 ml) heavy cream
- 1 tablespoon unsalted butter (for extra gloss, optional)
- Optional garnish: chopped peanuts, mini peanut butter cups, flaky sea salt
The base layer uses oil and hot liquid, a classic method for producing a moist, tender chocolate cake that stays soft even when chilled. The peanut butter layer is built like an American buttercream but with peanut butter as a co‑star, so it spreads easily and firms up in the refrigerator. The final chocolate topping is a standard ganache that sets into a sliceable, truffle‑like layer.
Instructions
Although the finished bars look layered and impressive, the process is straightforward when broken into three stages: bake the base, mix and spread the peanut butter layer, then pour on the chocolate topping. Cooling between each step is what keeps the layers clean and distinct.
Step 1: Make the Chocolate Cake Base
- Prepare your pan and oven.
Heat the oven to 350 °F (180 °C). Grease a 9×13‑inch baking pan, then line it with parchment paper, leaving a little overhang on two sides to act as handles. Lightly grease the parchment as well; this makes it much easier to lift the entire bar cake out for clean slicing. - Mix the dry ingredients.
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