¾ cup (≈150 g) light brown sugar, firmly packed
¾ tsp baking soda
¾ tsp salt
1 cup (≈237 ml) water
¾ cup (≈170 g) unsalted butter, cut into pieces
¼ cup (≈60 g) vegetable or canola oil
½ cup (≈145 g) creamy peanut butter (not natural‑style)
½ cup (≈118 ml) buttermilk
2 large eggs (room temperature)
1½ tsp vanilla extract
For the creamy PB frosting
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4 cups (≈500 g) powdered sugar
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½ cup (≈118 ml) buttermilk
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10 Tbsp (≈150 g) unsalted butter, cut into pieces
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⅔ cup (≈165 g) creamy peanut butter
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¼ heaping tsp salt
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1 tsp vanilla extract
Instructions
Step 1: Pre‑heat & prepare the pan
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Pre‑heat your oven to 350 °F (≈175 °C). Grease a 13×9‑inch baking pan (or equivalent) and optionally line with parchment for easier removal.
Step 2: Make the cake batter
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In a large bowl, whisk together the flour, granulated sugar, light brown sugar, baking soda and salt.
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In a medium saucepan over medium heat, combine water, butter pieces and oil. Bring to a boil. Once boiling, remove from heat and stir in peanut butter until fully melted and smooth.
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Pour the warm peanut butter mixture into the dry ingredients and stir to combine. Set aside to cool about 5‑10 minutes.
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In a separate bowl, whisk together buttermilk, eggs and vanilla extract. Then stir this mixture into the batter until just combined.
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Pour the batter into the prepared pan and smooth the top.
Step 3: Bake
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Bake for about 30‑32 minutes, or until a toothpick inserted in the center comes out clean or with moist crumbs (avoid over‑baking). Sugar Spun Run+1
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Remove from oven and allow to cool for ~10‑15 minutes while you prepare the frosting.
Step 4: Make the creamy PB frosting
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In a medium saucepan, combine buttermilk, butter pieces, peanut butter and salt. Cook over medium‑low heat, stirring until butter melts and mixture begins to boil. Remove from heat immediately.
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Add powdered sugar and vanilla extract. Whisk until smooth and pourable. Work quickly: the frosting will begin to set. Sugar Spun Run
Step 5: Frost & serve
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Pour the frosting evenly over the warm cake in the pan and use an offset spatula to spread it smoothly.
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Allow the frosting to cool and set before slicing. Once set, cut into ~24 squares and serve.
Tips for Success
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Avoid natural peanut butter (with separated oil) since it may affect texture and cause oily results. One recipe specifically advises against using it. Sugar Spun Run
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Ensure the peanut butter mixture is removed from heat as soon as it boils to prevent burning or separation. (For frosting step) Sugar Spun Run
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Don’t over‑bake the cake—sheet cakes are best when slightly moist in the center.
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Work quickly when pouring the frosting—once it begins to set it will thicken and may be harder to spread.
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For easier slicing, allow cake to cool completely and the frosting to set before cutting; then clean the knife between cuts for neat squares.
Variations
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Crunchy peanut butter version: Use crunchy peanut butter in the cake batter and/or swirl some peanut butter chips on top before frosting for texture.
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Peanut butter‑chocolate twist: Add ½ cup chocolate chips to the batter or drizzle melted chocolate over the frosting for a peanut butter‑chocolate combo.
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Smaller pan version: Use two 8‑inch or 9‑inch pans for thicker slices and shorter baking time (adjust accordingly). The Café Sucre Farine
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Lower‑sugar option: Use half the powdered sugar in the frosting and increase buttermilk slightly, though the result will be less set and more glaze‑like.
Storage & Reheating
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Storage: Cover the cake (in the pan or after slicing) and store at room temperature for up to 3 days. Though refrigeration isn’t necessary unless your room is very warm. Sugar Spun Run
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Freezing: Yes, you can freeze portions (well‑wrapped) for up to 2‑3 months. Thaw in fridge or at room temperature before serving.
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Reheating: If you like slightly warmed cake, microwave a slice for ~10‑15 seconds—frosting stays creamy and cake remains moist.
What to Serve With This Peanut Butter Sheet Cake with Creamy PB Frosting
Pairing ideas
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A glass of cold milk amplifies the richness and nostalgia.
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Serve alongside vanilla ice cream for extra indulgence.
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Fresh berries or sliced banana on the side bring a fruity contrast to the rich peanut flavour.
Presentation tip
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For gatherings, cut into neat squares, place on a platter and sprinkle chopped roasted peanuts or a drizzle of melted chocolate for a finishing touch.
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Use a foil‑lined pan for easy clean‑up and transport to potlucks.
