How to Make an Easy Peanut Butter Sheet Cake in a Jiffy

This easy peanut butter cake recipe takes less than an hour to make and is practically guaranteed to be a hit!

Peanut butter is the ultimate comfort food. Whether you spread it on toast, use it as a dip for apple slices or turn it into a delicious treat, we all have memories of snacking on PB. And when it comes to dessert, this easy peanut butter cake recipe is as simple as it gets. The cake is made right in a sheet pan for fast baking, simple serving and easy cleanup. You don’t even have to wait for the cake to cool to glaze it!

Here are more sheet cakes you’ll make again and again.

What Makes This Cake Unique

This cake is served right out of the sheet pan for a rustic, homey feel. It also takes way less time to make than most other cakes—it needs just 15 minutes of prep and 20 minutes of bake time.

But the most unique thing about this cake is the glaze. It’s not often you stir in marshmallows until they completely melt, but that’s what this recipe calls for. The marshmallows help the glaze set into a soft, rich texture that complements the smooth flavor of the peanut butter.

There is also buttermilk in this sheet cake. The slight tang of the buttermilk helps to elevate the heavy peanut butter and ultra-sweet glaze so the cake isn’t too filling. (If you have leftovers, try one of these other uses for buttermilk.)

How to Make an Easy Peanut Butter Sheet Cake

Ingredients

For the cake:

  • Cooking spray or butter to grease the pan
  • 2 cups all-purpose flour
  • 2 cups sugar
  • 1 teaspoon baking soda
  • 1/2 teaspoon salt
  • 1 cup water
  • 3/4 cup butter, cubed
  • 1/2 cup chunky peanut butter (this is our favorite brand)
  • 1/4 cup canola oil
  • 2 large eggs, room temperature
  • 1/2 cup buttermilk
  • 1 teaspoon vanilla extract

For the glaze:

  • 2/3 cup sugar
  • 1/3 cup evaporated milk
  • 1 tablespoons butter
  • 1/3 cup chunky peanut butter
  • 1/3 cup miniature marshmallows
  • 1/2 teaspoon vanilla extract

Note: Reduced-fat peanut butter is not recommended for this recipe.

Step 1: Prepare the Pan

Preheat your oven to 350°. Use cooking spray or melted butter to grease a 15×10-inch baking pan.

Editor’s Tip: If you don’t have this size, you can substitute a more common 13×9-inch pan. Just know that the baking time will vary and your pan will be quite full.

Step 2: Make Your Mixes

In a large bowl, whisk together the flour, sugar, baking soda and salt. Set aside. In a small bowl, whisk the eggs, buttermilk and vanilla until blended. Set aside.

In a small saucepan, combine the water and butter. Bring the mixture just to a boil, then stir in the peanut butter and oil until blended.

Step 3: Put It All Together

Add the warm peanut butter mixture to the flour mixture and whisk until well-combined. Once the mixture is fully integrated, add the buttermilk mixture and whisk until smooth.

Editor’s Tip: Be careful not to overmix in this step. The whisking encourages gluten formation and too much gluten can make a cake dense and gummy instead of light and springy.

Step 4: Bake It

Pour the batter into your prepared pan. Place on the middle rack of the oven and bake for 10 minutes.

Rotate the pan and bake an additional 10-12 minutes or until a toothpick inserted into the center of the cake comes out clean.

Step 5: Glaze Time!

While the cake is baking, combine the sugar, milk and butter in a saucepan over medium heat. Stir constantly as the mixture comes to a boil. Once boiling, cook for two minutes, then remove from heat and stir in peanut butter, marshmallows and vanilla until blended. Spoon the glaze over the warm cake, spreading evenly. Cool on a wire rack and allow the glaze to set.

Editor’s Tip: If you’re a frosting fan, you can double the ingredients for the glaze for an extra-thick layer of peanut butter and marshmallow goodness.

Make it Your Own!

This cake can be customized by adding chocolate chips to the cake batter, the glaze or—for the real chocolate lovers out there—both! You can also sprinkle crushed peanuts on the cake for a little extra crunch.

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Mandy Naglich
Mandy is a food and beverage writer with bylines at WNYC, Munchies, Mic and October. She's a Certified Cicerone and award-winning homebrewer living, writing and cooking in New York City.