Peanut Butter Sheet Cake

This cake is a peanut butter lover’s dream. Soft, fluffy, and slathered in warm peanut butter frosting. It’s simple, rich, and totally unforgettable.

I baked it for a family get-together, and everyone wanted seconds and the recipe. The cake stays super moist, and the frosting? Smooth, sweet, and melts right into every bite.

It’s sweet, salty, and perfect for feeding a crowd. No layers, no fuss—just pure peanut butter comfort. One pan, endless happiness.

Let’s make it happen! This peanut butter sheet cake is easy, cozy, and always a hit. Grab your mixing bowl—this one’s a keeper.

Why You’ll Love This Recipe

• Deep Peanut Butter Flavor: There’s peanut butter in the batter and the frosting, but it’s not overpowering. It’s smooth, mellow, and comforting—like peanut butter toast, but way better.
• Foolproof Texture: The combination of oil, butter, and buttermilk creates a cake that stays moist for days without becoming greasy. It’s soft and slightly springy, just the way a good sheet cake should be.
• One Bowl Simplicity: You’ll make the batter right on the stovetop. No stand mixer. No special techniques. Just heat, whisk, and pour.
• Crowd-Friendly: The 13×9 size means it feeds a small crowd with zero stress. It travels well and cuts cleanly—perfect for potlucks or meal trains.

What You Need to Know Before You Start

Prep Time & Cook Time:

• Prep Time: 20 minutes
• Cook Time: 25–28 minutes
• Cool Time: 15 minutes before frosting
• Total Time: Just under 1 hour

Servings:
You’ll get 12 generous slices or up to 16 smaller squares. The texture is sturdy enough to eat out of hand, but soft enough to still feel like a special treat.

Difficulty:
Easy. This is a beginner-friendly recipe that delivers big results. The stovetop mixing process means fewer dishes and less fuss.

Flavor Profile:
This cake tastes like a cross between a peanut butter cookie and a yellow cake, but with a lighter crumb and more richness. The frosting adds a hit of salty-sweet indulgence.

Storage Tip:
The cake stays fresh for 3–4 days at room temperature if covered tightly. The frosting locks in moisture, so no need to refrigerate unless your kitchen is very warm.

Required Kitchen Tools

You won’t need much—this is a minimalist baker’s dream:

• 13×9-inch metal baking pan (avoid glass, which may bake unevenly)
• Medium saucepan (for stovetop batter and frosting prep)
• Whisk or silicone spatula
• Large mixing bowl
• Wire rack (to cool the cake evenly)
• Offset spatula (optional) if you want to smooth the frosting

Ingredients for the Peanut Butter Sheet Cake

Let’s break down what each ingredient does and why it matters:

• All-purpose flour (2 cups): The base. Too much will make the cake dry—so spoon and level, don’t scoop.
• Granulated sugar (1 cup) + Light brown sugar (¾ cup): The combo adds structure, sweetness, and just a touch of molasses depth from the brown sugar.
• Baking soda (¾ tsp): This reacts with the buttermilk to lift the cake and give it a slightly tender chew.
• Salt (¾ tsp): It won’t make the cake salty—it just wakes up the peanut butter and balances the sugar.
• Water (1 cup): Sounds odd, but it helps dissolve the sugars when mixed hot and keeps the batter fluid.
• Unsalted butter (¾ cup / 170g): Adds richness and that familiar buttery flavor.
• Neutral oil (¼ cup): Prevents the cake from drying out over time.
• Creamy peanut butter (½ cup): Choose a processed, shelf-stable type like Jif or Skippy—not natural or oily.
• Buttermilk (½ cup): Essential for moisture and acidity. If you don’t have it, stir 1½ teaspoons vinegar into whole milk and let it sit for 5 minutes.
• Eggs (2 large): Room temp works best so they mix in evenly.
• Vanilla extract (1½ tsp): Enhances the overall warmth and brings the flavors together.

Ingredients for the Fudgy Peanut Butter Frosting

This warm frosting is spread immediately after baking—don’t wait for the cake to cool all the way. It melts into the top layer and creates a silky shell on the surface as it sets.

• Powdered sugar (4 cups): Sift it first to avoid clumps and get that velvety texture.
• Buttermilk (½ cup): This makes the frosting tangy and pourable—much smoother than using milk alone.
• Unsalted butter (10 Tbsp): It gives body and keeps the frosting from crusting too quickly.
• Creamy peanut butter (⅔ cup): Use the same type you used in the cake for consistent flavor.
• Salt (¼ tsp): Optional, but a tiny pinch makes the sweet and nutty flavor pop.
• Vanilla extract (1 tsp): Rounds out the richness with a little floral note.

Variations for Peanut Butter Sheet Cake

• Chocolate Peanut Butter Twist: Add ½ cup mini chocolate chips to the batter or drizzle melted chocolate over the frosting once set.
• Crunchy Topping: Sprinkle chopped salted peanuts or crushed pretzels over the warm frosting for texture.
• Banana Peanut Butter Cake: Replace ¼ cup of buttermilk with mashed ripe banana for a hint of fruitiness.
• Nut-Free Option: Use sunflower seed butter in place of peanut butter. It will change the flavor slightly, but still tastes rich and delicious.
• Peanut Butter & Jelly Sheet Cake: Swirl a few tablespoons of raspberry or strawberry jam into the frosting just before spreading it onto the cake.

How to Make Peanut Butter Sheet Cake

Step-by-Step Instructions

1. Preheat and Prep

Preheat your oven to 350°F (175°C).
Grease a 13×9-inch metal baking pan with butter or nonstick spray. Set aside.

2. Mix the Dry Ingredients

In a large mixing bowl, whisk together:

• 2 cups all-purpose flour
• 1 cup granulated sugar
• ¾ cup light brown sugar
• ¾ teaspoon baking soda
• ¾ teaspoon salt

Set aside.

3. Heat the Wet Ingredients on the Stove

In a medium saucepan over medium heat, combine:

• 1 cup water
• ¾ cup unsalted butter (cut into chunks)
• ¼ cup neutral oil
• ½ cup creamy peanut butter

Warm the mixture, stirring often, until the butter and peanut butter melt and the mixture just begins to bubble gently around the edges (don’t let it boil). Once smooth, remove from heat.

4. Combine Wet and Dry

Pour the warm peanut butter mixture into the bowl with the dry ingredients. Whisk or stir until just combined.

5. Add Eggs, Buttermilk, and Vanilla

To the slightly cooled batter, add:

• ½ cup buttermilk
• 2 large eggs
• 1½ teaspoons vanilla extract

Mix gently until smooth and cohesive. Do not overmix.

6. Bake the Cake

Pour the batter into your prepared pan.
Tap the pan gently on the counter to release air bubbles.

Bake for 25–28 minutes or until a toothpick inserted in the center comes out clean or with a few moist crumbs. The cake should be lightly golden on top and springy to the touch.

Place the cake on a wire rack and let it cool for about 15 minutes while you make the frosting.

How to Make the Fudgy Peanut Butter Frosting

1. Heat the Frosting Base

In a clean medium saucepan over medium heat, combine:

• 10 tablespoons unsalted butter
• ½ cup buttermilk
• ⅔ cup creamy peanut butter

Stir constantly until melted and smooth. Do not let it boil.

2. Add Powdered Sugar and Vanilla

Remove the pan from heat. Immediately whisk in:

• 4 cups sifted powdered sugar
• 1 teaspoon vanilla extract
• Optional: ¼ teaspoon salt

Whisk until silky and spreadable. The frosting should be warm and pourable but not runny. If too thick, add a splash more buttermilk.

3. Frost the Cake

Pour the warm frosting over the still-warm cake.
Use an offset spatula or the back of a spoon to gently spread it evenly to the edges.

Let the cake rest at room temperature for about 30 minutes so the frosting can set into a soft, slightly glossy layer.

Serving and Decoration

You can serve this cake slightly warm or at room temperature. For extra appeal:

• Dust lightly with flaky sea salt just before serving to contrast the sweetness.
• Top with crushed peanuts or mini chocolate chips if you want a bit of texture.
• Serve with coffee or cold milk—the salty-sweet richness pairs perfectly with both.

This cake cuts cleanly once cooled, making it ideal for bake sales, school events, or meal trains.

Storing Peanut Butter Sheet Cake

• Room Temperature: Store the cake tightly covered with plastic wrap or in an airtight container for up to 4 days. The frosting keeps it moist.
• Refrigeration: Optional, but helpful in warmer climates. If chilled, let it sit at room temp for 20–30 minutes before serving so the frosting softens.
• Freezing: You can freeze individual slices. Wrap tightly in plastic wrap, then foil, and store in a freezer-safe bag for up to 2 months. Thaw overnight in the fridge.

Tips and Tricks for Success

• Use processed peanut butter like Jif or Skippy. Natural peanut butter can separate and affect the texture.
• Don’t skip the buttermilk. It adds tenderness and a subtle tang that balances the sweetness.
• Whisk while warm. Both the cake batter and frosting come together best when the mixtures are warm—don’t wait too long.
• Frost while warm. Pouring the frosting on a warm cake helps it melt in and stick, creating that gooey top layer.
• Use a metal pan for even heat distribution and proper rise. Glass pans can cause the edges to overbake.

Nutrition (per serving, based on 16 servings)

Nutrient	Amount
Calories	~360 kcal
Carbohydrates	40–42 g
Protein	6 g
Fat	20 g
Saturated Fat	6 g
Cholesterol	45 mg
Sodium	210 mg
Sugar	28 g
Fiber	1–2 g
Calcium	30 mg
Iron	1.3 mg

Note: Nutrition may vary depending on ingredient brands used.

Peanut Butter Sheet Cake FAQs

Can I use crunchy peanut butter?
Yes, but it will change the texture slightly. Smooth peanut butter creates a softer, more uniform crumb.

Can I halve this recipe?
Yes, bake in an 8×8 or 9×9-inch pan. Reduce baking time to around 20 minutes.

What if I don’t have buttermilk?
Stir 1½ teaspoons white vinegar or lemon juice into ½ cup whole milk. Let sit for 5 minutes.

Can I make this ahead?
Absolutely. Make it the night before and store tightly wrapped. The flavor is even better the next day.

Conclusion

This Peanut Butter Sheet Cake is a classic in every sense: easy to make, deeply satisfying, and just sweet enough. It delivers that nostalgic, homemade flavor you only get from baking something simple and sincere. Whether you’re taking it to a gathering or just cutting yourself a quiet slice after dinner, this cake offers comfort in every bite.

The warm frosting, the soft crumb, the richness of peanut butter—it all works together without being fussy. It’s the kind of recipe you’ll come back to, not just because it tastes good, but because it feels like home.