Easy Peanut Butter Sheet Cake with Chocolate Frosting

There are few flavor combinations as universally loved as chocolate and peanut butter. It’s a nostalgic duo that brings back childhood memories while satisfying our most decadent dessert cravings. This Peanut Butter Sheet Cake is the ultimate celebration of that perfect pair. It’s a ridiculously moist, tender peanut butter cake baked in a simple sheet pan, slathered with a rich, creamy chocolate peanut butter frosting, and finished with a festive crunch of mini M&M’s. It’s the kind of dessert you bring to a potluck and leave with an empty pan and a dozen requests for the recipe.

Unlike complicated layer cakes, this sheet cake is straightforward, unfussy, and designed to feed a crowd. The batter comes together in minutes, and the frosting is a dreamy, whipped concoction that’s simply irresistible. Whether it’s for a birthday party, a family gathering, or just a Tuesday that needs a little something special, this cake always delivers.

Table of Contents

Why make this Peanut Butter Sheet Cake Recipe

If you’re not already convinced, here are a few more reasons why this Peanut Butter Sheet Cake needs to be on your baking list:

• Feeds a Crowd: Baked in a quarter sheet pan, this recipe yields about 20 generous servings, making it the perfect dessert for parties and gatherings.
• Incredibly Moist: Thanks to the combination of brown sugar, whole milk, and plenty of peanut butter, this cake has a tender, moist crumb that stays fresh for days.
• Easy & Approachable: No fancy techniques or equipment needed! This is a simple mix-and-bake recipe that delivers impressive results with minimal effort.
• The Ultimate Frosting: The frosting isn’t just an afterthought; it’s a star. Made with real melted milk chocolate and a hint of peanut butter, it’s fudgy, creamy, and absolutely divine.
• Fun and Customizable: Mini M&M’s add a fun pop of color and crunch, but you can easily swap them for chopped peanuts, Reese’s Pieces, or your favorite sprinkles!

Ingredients

• 1 cup (2 sticks) unsalted butter, room temperature
• 1 cup brown sugar
• 1/2 cup granulated sugar
• 1 cup smooth peanut butter
• 1 teaspoon vanilla extract
• 3 large eggs, room temperature
• 2 teaspoons baking powder
• 1/4 teaspoon salt
• 2 and 1/4 cups all-purpose flour
• 1 cup whole milk
• 1/2 cup (1 stick) unsalted butter, room temperature
• 1 cup good-quality milk chocolate
• 3 cups powdered sugar, sifted
• 2-3 tablespoons whole milk, room temperature
• 1 tablespoon smooth peanut butter
• 1 cup mini M&M’s

How to make Peanut Butter Sheet Cake

Step 1: First, get your oven and pan ready. Preheat the oven to 350°F. Grease a quarter sheet pan and line it with parchment paper, leaving a little overhang on the sides to make lifting the cake out easier later.

Step 2: In a large mixing bowl, combine the room temperature butter, brown sugar, and granulated sugar. Using an electric mixer on medium speed, beat them together until the mixture is light, pale, and creamy. Scrape down the sides of the bowl, then add the peanut butter and vanilla extract. Mix again until everything is smooth and well combined.

Step 3: Add the eggs one at a time, beating on a low speed just until each one is incorporated. The mixture might look a bit curdled or separated at this stage—don’t worry, this is completely normal and it will all come together.

Step 4: In a separate small bowl, you can whisk the baking powder and salt into the flour. Add half of this flour mixture to the wet ingredients, followed by all of the milk. Beat on low speed until just combined. Add the remaining flour and mix again on low until you have a thick, smooth batter. Be careful not to overmix.

Step 5: Pour the batter into your prepared sheet pan and spread it out evenly with a spatula. Bake for 35-40 minutes. The cake is done when it’s golden brown and a skewer inserted into the center comes out clean. Let the cake cool completely in the pan before you even think about frosting it.

Step 6: While the cake cools, start the frosting. Melt the milk chocolate in the microwave in 20-second bursts, stirring in between, until it’s smooth. Set it aside to cool down slightly. Meanwhile, in a large mixing bowl, beat the 1/2 cup of room temperature butter with an electric mixer for a couple of minutes until it’s very pale and creamy.

Step 7: Add half of the sifted powdered sugar and one tablespoon of milk to the whipped butter. Beat on low speed until the sugar is incorporated. Add the rest of the powdered sugar and another tablespoon of milk, mixing on low again. Once combined, turn the speed up to medium and beat for another minute until fluffy.

Step 8: Pour the cooled, melted chocolate and the tablespoon of peanut butter into the buttercream. Beat until everything is fully mixed and the frosting is smooth and luscious. If it seems too thick, mix in one more tablespoon of milk. Generously spread the frosting over the completely cooled cake, scatter the mini M&M’s on top, slice, and serve!

How to serve Peanut Butter Sheet Cake

This cake is a star all on its own, but it’s fantastic served with a tall glass of cold milk or a simple cup of coffee. For an extra decadent treat, serve a warm slice with a scoop of vanilla bean ice cream and a drizzle of chocolate sauce. It’s the perfect dessert to slice into squares and arrange on a platter for easy self-serving at parties.

How to store Peanut Butter Sheet Cake

Store any leftover cake in an airtight container at room temperature for up to 3 days. If your kitchen is particularly warm, you may want to refrigerate it to keep the frosting firm. If refrigerated, let it sit at room temperature for about 20-30 minutes before serving to allow the cake and frosting to soften. You can also freeze individual slices wrapped tightly in plastic wrap and then foil for up to 3 months.

Tips to make Peanut Butter Sheet Cake

Use Room Temperature Ingredients: This is non-negotiable for a smooth, emulsified batter and frosting. Butter, eggs, and milk should all be at room temperature to combine properly.

Don’t Overmix: Once you add the flour, mix only until it’s just combined. Overmixing develops the gluten and can lead to a tough, dense cake.

Cool Completely: Be patient! If you try to frost a warm cake, you’ll have a melty, soupy mess. The cake must be completely cool to the touch.

Use Good Quality Chocolate: The flavor of the frosting really shines, so use a good quality milk chocolate that you would enjoy eating on its own.

Easy Pan Prep: Leaving a parchment paper “sling” with overhang on two sides makes it incredibly easy to lift the entire cake out of the pan for clean, perfect slicing.

If you enjoy the simple, crowd-pleasing nature of a good sheet cake, you will absolutely love my Brown Butter Pumpkin Sheet Cake, which is perfect for fall festivities!

FAQs About Peanut Butter Sheet Cake

Can I use crunchy peanut butter?

You can, but it will change the texture of the cake, making it a bit more dense and nutty. For the smoothest cake and frosting, standard smooth peanut butter (like Jif or Skippy) is recommended over natural-style peanut butter, which can be oily.

What can I use instead of M&M’s?

So many options! Try chopped Reese’s Peanut Butter Cups, Reese’s Pieces, chocolate sprinkles, rainbow sprinkles, chopped roasted peanuts, or a drizzle of melted peanut butter for a different look and taste.

Can I make this cake ahead of time?

Absolutely. You can bake the cake layer a day in advance, let it cool, and cover it tightly. Make the frosting and frost the cake the day you plan to serve it for the best results. The fully frosted cake also holds up well for a day at room temperature.

Hungry for more? Follow us on Pinterest for daily recipes!

Final Thoughts

This Peanut Butter Sheet Cake is pure comfort in dessert form. It’s rich, satisfying, and has that perfect balance of sweet and salty that makes the chocolate and peanut butter combination so iconic. It’s a recipe that’s sure to become a family favorite, requested for every occasion. This is a guaranteed hit, but if you’re looking for another amazing chocolate and peanut butter combination, don’t miss my Chocolate Peanut Butter Poke Cake Recipe. Enjoy every single bite!

Print