Decadent Peanut Butter Sheet Cake — Fudgy, Nutty & Crowd-Pleasing

Peanut Butter Sheet Cake is one of those desserts that shows up at potlucks and family dinners and instantly gets that “who brought this?” look — and for good reason. It’s moist, nutty, and downright addictive, topped with a glossy peanut-butter frosting that sets this sheet cake apart from the pack.

Why you’ll fall hard for this cake

You want a simple, crowd-pleasing dessert that actually tastes like it took effort? This is it. The cake comes together in one shallow pan, bakes fast, and the warm, fudgy frosting soaks in slightly for that nostalgic, bakery-style finish. Think classic comfort with a grown-up peanut butter twist.

Bold tip: use quality peanut butter (not the oil-separated natural kind) for best texture and flavor in both the batter and the frosting.

The Key Ingredients (and Why You Need Them)

Below I list the main ingredients (no amounts here — the printable card has those). I’ll explain what role each plays so you understand how and why to tweak things.

• All-purpose flour — gives structure. Don’t swap in too much whole-wheat or the texture will change.
• Granulated sugar — sweetens and feeds browning. You can reduce slightly, but expect a change in crust and flavor.
• Baking soda — provides lift and a fine crumb.
• Salt — balances sweetness and enhances peanut flavor.
• Water & buttermilk — the combo keeps the cake tender and moist; buttermilk adds subtle tang and reacts with the baking soda for leavening.
• Butter + vegetable oil — fat = flavor and tenderness. Butter gives the classic baked-good flavor while oil keeps the cake soft for days.
• Peanut butter — obviously the star. It adds nutty richness and depth to the batter and the frosting.
• Eggs — bind the batter and add structure.
• Evaporated milk & marshmallows (in the frosting) — evaporated milk gives body and caramel notes to the frosting; marshmallows melt down to make the frosting velvety and slightly gelatinous.
• Vanilla extract — brings everything together and brightens the flavor.

How to Make It

Follow these production-tested steps for a flawless sheet cake every time.

1. Preheat and prep

Preheat your oven to 350°F (175°C). Grease a 10×15×1-inch jelly-roll pan thoroughly — you want even coverage so the cake releases cleanly. Lightly dust with flour or use parchment if you prefer.

2. Dry mix

Whisk together the flour, sugar, baking soda, and salt in a large bowl. This ensures even distribution of leavening and salt so the cake bakes uniformly.

3. Make the hot peanut base

In a small saucepan, bring water and the specified butter to a boil. Remove from heat and whisk in the peanut butter and vegetable oil until the mixture becomes smooth and glossy. This hot liquid does two things: it melts any sugar clumps and helps create a tender crumb once mixed with the dry ingredients.

4. Combine wet and dry

Pour the hot peanut mixture into the dry ingredients and stir to incorporate. Separately, whisk the eggs, buttermilk, and vanilla, then fold that into the batter until just combined. Do not overmix — overworked batter yields a tough cake.

5. Bake

Spread the batter evenly in your prepared jelly-roll pan. Bake for about 18–26 minutes, depending on your oven, until a toothpick inserted near the center comes out clean. The cake should spring back lightly to the touch.

Bold tip: check early — sheet cakes can go from perfect to dry fast. Start testing when the lower end of the time range arrives.

6. Make the frosting while the cake bakes

Combine the sugar, evaporated milk, and butter in a saucepan and bring to a boil, stirring constantly. Let the mixture cook, stirring, for 2 minutes to develop a slightly caramelized edge. Remove from heat and immediately stir in the peanut butter, marshmallows, and vanilla until smooth and uniform. The marshmallows melt into the hot mixture and help create a glossy, slightly chewy frosting.

7. Finish and set

Spoon the warm frosting over the hot cake and spread into an even layer. The heat allows the frosting to sink slightly into the cake, which gives the dessert that nostalgic, bakery-style finish. Let the cake cool completely before slicing — this helps the frosting set and makes clean slices.

Pro tips for perfect results

• Room-temperature eggs mix more easily and incorporate better into the batter.
• Measure flour properly — spoon into the cup and level off. Packing flour makes cake dense.
• Use an instant-read thermometer for confidence; internal temperature for a sheet cake isn’t as reliable, but the toothpick test works great.
• Don’t skip the marshmallows — they give the frosting a nostalgic fluff and silky texture that straight peanut-butter-candy frosting won’t.
• If you want a prettier finish, drizzle fudge or chocolate sauce in stripes over the frosting while it’s still warm for a swirl effect. This creates an almost fudgy accent without extra fuss.
• Store at room temp if your kitchen is cool; otherwise refrigerate and bring to room temp before serving for best flavor.

Bold tip: let the cake cool just enough so the frosting sets but is still soft — this helps that perfect glossy sheen.

Easy variations to try

Want to switch the vibe? Try one of these:

• Peanut Butter Sheet Cake With Chocolate Chips: fold miniature chocolate chips into the batter for delightful pockets of melty chocolate. (Yes, please.)
• Old-Fashioned Peanut Butter Sheet Cake: swap evaporated milk in the frosting for a dollop of heavy cream for a richer, old-school finish.
• Chocolate And Peanut Butter Texas Sheet Cake riff: make a chocolate sheet cake base and use this peanut butter frosting for a Texas-sized flavor bomb. That mash-up hits nostalgic notes and modern cravings at once.
• Pudding twist: stir a scoop of instant vanilla pudding into the batter to add moistness and a slightly denser crumb — a neat little trick for busy bakers. This nod to Puddings gives you extra stability and mouthfeel.
• No-marshmallow frosting: if marshmallows aren’t your jam, replace with ⅓ cup creamy peanut butter and a few tablespoons of powdered sugar to thicken.

How to serve (presentation ideas)

• Cut into squares and serve on a platter for potlucks. This cake is designed to feed a crowd.
• For parties, garnish slices with crushed peanuts and a light drizzle of fudge or salted caramel.
• Serve warm or at room temperature — both work. If chilled, allow slices to come to room temp for better peanut-butter flavor.
• Add a scoop of vanilla ice cream for a decadent dessert plate.

Storage & leftovers

• Room temperature: cover loosely and store up to 2 days in a cool kitchen.
• Refrigerator: place in an airtight container and chill up to 5 days. Bring to room temp before serving.
• Freezing: wrap individual pieces tightly in plastic wrap, then foil; freeze up to 2 months. Thaw overnight in the fridge.

Bold tip: freeze in single portions for easy grab-and-go treats or for stashing in the freezer for unexpected guests.

FAQs — quick answers

Why this belongs in your rotation of Sheet Cake Recipes

This cake is fast, forgiving, and nostalgic — exactly the kind of dessert you want when feeding a crowd. It hits the sweet spot between Old Fashioned Peanut Butter Sheet Cake vibes and modern twists, while still being approachable for novice bakers. Plus, it pairs beautifully with coffee, milk, or a scoop of vanilla ice cream.

Final thoughts — make it your signature

Whether you want a classic Peanut Butter Sheet Cake for a family potluck or to try a playful Banana pudding twist (see “puddings” above for inspiration), this recipe is a reliable winner. It’s scalable, adaptable, and genuinely loved by kids and adults alike.

So, ready to make this? Preheat that oven, warm up the peanut butter, and prepare for compliments.

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