Name: Peanut Butter Sheet Cake
Prep time: 15 min
Cook time: 15 min
Total time: 30 min
Cuisine: American
Ingredients: ¼ cup creamy peanut butter; 1 cup water; ½ cup butter; 1 cup sugar; 1 cup brown sugar; 2 cups flour; 1 teaspoon salt; 1 teaspoon baking soda; 2 eggs; ½ cup buttermilk (or substitute); 1 teaspoon vanilla; ¾ cup butter (for frosting); 6 Tbsp buttermilk (for frosting); ½ cup peanut butter (for frosting); 3½ cups powdered sugar; 1 Tbsp vanilla (for frosting)

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A moist and flavorful peanut butter sheet cake topped with a rich, creamy peanut butter frosting. Baked in a sheet pan for easy slicing and serving, this dessert is perfect for potlucks, parties, or whenever I’m craving something indulgent but easy to whip up.

Why You’ll Love This Recipe

I love how simple and fuss-free this recipe is. The cake is incredibly soft, with just the right balance of sweetness and peanut butter flavor. The warm frosting poured over the still-warm cake sinks in slightly, creating a melt-in-your-mouth texture that’s completely irresistible. Plus, it’s all done in one pan, making cleanup a breeze and serving a crowd effortless.

Ingredients

(Here’s a tip: Check out the full list of ingredients and measurements in the recipe card below.)

¼ cup creamy peanut butter
1 cup water
½ cup butter
1 cup sugar
1 cup brown sugar
2 cups flour
1 teaspoon salt
1 teaspoon baking soda
2 eggs
½ cup buttermilk (or substitute)
1 teaspoon vanilla

For the frosting:

¾ cup butter
6 Tbsp buttermilk
½ cup peanut butter
3½ cups powdered sugar
1 Tbsp vanilla

Directions

I preheat the oven to 375 °F (190 °C).
In a medium saucepan, I combine ¼ cup peanut butter, water, and ½ cup butter. I bring it to a boil, then remove it from the heat.
In a large bowl, I stir together sugar, brown sugar, flour, salt, and baking soda.
I pour the warm peanut butter mixture into the dry ingredients and stir well.
I add eggs, buttermilk, and vanilla, mixing until everything is well combined.
I pour the batter into a greased or parchment-lined 12×17 sheet pan and bake for 13–15 minutes, keeping a close eye not to overbake.
While the cake bakes, I prepare the frosting. In a small saucepan, I bring together ¾ cup butter, 6 Tbsp buttermilk, and ½ cup peanut butter until it boils.
I remove the mixture from heat and stir in the powdered sugar and vanilla until smooth.
I pour the warm frosting over the freshly baked, warm cake and spread it evenly.

Servings and timing

This recipe makes about 16 servings, perfect for a crowd or for enjoying over a few days. The total time from start to finish is just 30 minutes — 15 minutes for prep and 15 minutes to bake. It’s a quick dessert I can pull together without much effort.

Variations

I sometimes use crunchy peanut butter for added texture in the cake and frosting.
For a chocolate-peanut butter twist, I sprinkle mini chocolate chips over the frosting while it’s still warm.
I’ve also topped it with chopped roasted peanuts for a bit of crunch.
A swirl of jam in the batter before baking gives it that nostalgic PB&J vibe.
If I want to cut the sweetness slightly, I reduce the powdered sugar in the frosting by half a cup.

storage/reheating

I store the cake covered at room temperature for up to 3 days, or in the fridge for up to 5 days. If I want that freshly-baked warmth, I microwave individual slices for 10–15 seconds. This softens the frosting and brings back that just-out-of-the-oven feel. The cake also freezes well — I wrap slices individually and store them in a sealed container for up to 2 months.

FAQs

How do I substitute buttermilk if I don’t have any?

I add 1 tablespoon of lemon juice or white vinegar to a measuring cup, then fill it with milk to reach ½ cup. After letting it sit for 5 minutes, it’s ready to use in place of buttermilk.

Can I make this cake ahead of time?

Yes, I often bake the cake a day in advance. I cover it tightly and store it at room temperature, then frost it just before serving or frost it while warm and store it already frosted.

What kind of peanut butter works best?

I use creamy commercial peanut butter like Jif or Skippy. Natural peanut butter can work, but I make sure it’s well-stirred and not too oily or dry, as that can affect the texture.

Can I use a different pan size?

A 12×17 sheet pan gives the best thin, soft cake texture, but I’ve also used a 9×13 pan for a thicker cake. I just adjust the baking time to around 20–25 minutes and check for doneness.

How do I know when the cake is done baking?

I look for the top to spring back lightly when touched, and a toothpick inserted should come out with a few moist crumbs — not wet batter. I’m careful not to overbake, as the cake stays moist when baked just right.

Conclusion

This peanut butter sheet cake is one of my favorite quick desserts to make when I want something cozy, nostalgic, and totally satisfying. With a moist, peanutty base and that irresistible pour-on frosting, it’s always a hit — whether I’m sharing it with guests or sneaking a slice for myself with a cup of coffee.