Peanut Butter Cake

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A soft, tender peanut butter sheet cake topped with warm, pour-on peanut butter icing that sets into a smooth, crackly glaze. Big flavor, easy prep, no mixer needed.

Prep Time20

Cook Time35

Total Time55

Course: Cake and Cupcakes, Dessert

Cuisine: American

Keyword: peanut butter cake, peanut butter sheet cake

Servings: servings

Author: Dahn Boquist

Ingredients

Cake

2 cups all-purpose flour 240 grams
2 cups brown sugar packed, 426 grams
1 teaspoon baking soda
½ teaspoon baking powder
1 teaspoon salt
⅔ cup creamy peanut butter regular commercial style, not natural, 180 grams
1 cup water 227 grams
8 tablespoons butter 113 grams
½ cup vegetable oil 100 grams
½ cup buttermilk room temperature, 119 grams
2 large eggs
2 teaspoons vanilla extract

Icing

1 cup creamy peanut butter 270 grams
12 tablespoons butter 170 grams
½ cup whole milk 120 grams grams
2 teaspoons vanilla extract
½ teaspoon salt
3 ½ cups powdered sugar
Reese’s Mini Peanut Butter Cups chopped, for garnish (optional)

Instructions

Preheat oven to 350°F. Grease a 9x13-inch baking pan or line it with parchment paper.
In a large bowl, whisk together the flour, brown sugar, baking soda, baking powder, and salt.
In a saucepan over medium heat, combine the water, peanut butter, oil, and butter. Heat, stirring, until the mixture is melted and smooth. You don’t need a hard boil, just hot and fully blended.
Remove the pan from the heat. Add the buttermilk and stir to cool the mixture slightly (it should feel warm but not hot to the touch). Then whisk in the eggs and vanilla until smooth.
Pour the warm peanut butter mixture into the flour mixture. Stir until smooth and there are no flour streaks in the batter.
Pour the batter into the prepared pan and spread evenly. Bake for 35–40 minutes, until the top looks set and a toothpick in the center comes out clean.
Set the warm cake on a rack while you make the icing. Leave the cake in the pan. The warm icing is thin and pourable at first, and the pan helps contain it so it spreads into a smooth, even layer before setting.

Icing

Melt the peanut butter and butter in a saucepan over medium heat; stir until smooth. Keep the heat moderate and don’t let it boil, just warm enough to melt everything together. Mix in the milk, vanilla, and salt until combined.
Remove the pan from the heat, then whisk in the powdered sugar until smooth, 3 to 5 minutes.
Pour the icing over the warm cake and spread evenly. Let the cake and icing cool completely before slicing.
If desired, sprinkle chopped peanut butter cups over the icing while it's still slightly warm so they stick.

Notes

Use regular peanut butter: Natural or “stir” brands can separate and cause the batter or icing to turn oily or gritty. Stick with commercial peanut butter like Jif or Skippy for smooth, reliable results.

Don’t boil the icing base: Keep it warm enough to melt, but not bubbling, to prevent curdling.

Cool slightly before adding eggs: The peanut butter mixture should feel warm, not hot, to avoid scrambling the eggs.

Pour the icing while warm: It spreads smoothly and sets into a candy-like glaze as it cools.

Storage: Cover and store at room temperature for up to 3 days, or refrigerate for up to 5 days.

Freezer-friendly: Once cooled, wrap the whole cake tightly in plastic wrap and foil. Freeze for up to 2 months. Thaw at room temperature before serving.

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