Name: Decadent Chocolate Mayonnaise Sheet Cake Recipe
Prep time: 20 min
Cook time: 30 min
Total time: 1 h 20 min
Cuisine: American
Ingredients: Butter, for greasing the pan; 2 cups (242g) all-purpose flour; 1 cup (120g) unsweetened Dutch processed cocoa powder; 1 1/2 teaspoons baking powder; 1 1/2 teaspoons baking soda; 1/4 teaspoon salt; 3/4 cup (177ml) hot water; 2 tablespoons (30g) instant coffee powder or instant espresso powder; 2 large eggs; 1 cup (220g) sugar; 1/2 cup (100g) brown sugar, lightly packed; 1 cup (260g) mayonnaise; 1 tablespoon vanilla extract; 1/2 cup (80g) finely chopped semisweet or bittersweet chocolate; 1/2 cup (113g) unsalted butter; 2 tablespoons (30g) unsweetened Dutch processed cocoa powder; 1 cup (130g) powdered sugar; 1/2 cup heavy cream

There’s something so irresistibly rich and moist about this Decadent Chocolate Mayonnaise Sheet Cake Recipe that makes it a beloved classic in my kitchen. The secret ingredient—mayonnaise—keeps it unbelievably tender and fudgy, turning an everyday sheet cake into a showstopper.

The image shows a clear glass baking pan with a thick, dark brown chocolate cake inside. The cake has a smooth, shiny layer of light brown chocolate frosting spread evenly on top. Three square pieces are cut from the cake and are lying next to the cake inside the pan, showing the dense, moist texture of the dark cake beneath the frosting. The background has a white marbled texture. photo taken with an iphone --ar 2:3 --v 7

Jump to:

Why You'll Love This Recipe
Ingredients & Why They Work
Make It Your Way
Step-by-Step: How I Make Decadent Chocolate Mayonnaise Sheet Cake Recipe
Top Tip
How to Serve Decadent Chocolate Mayonnaise Sheet Cake Recipe
Make Ahead and Storage
Frequently Asked Questions:
Final Thoughts
Decadent Chocolate Mayonnaise Sheet Cake Recipe

Why You'll Love This Recipe

This cake is a perfect blend of simplicity and indulgence. I’m always amazed how mayonnaise can work wonders in baking—adding moisture without any weird flavors. You’ll be amazed how easy it is to whip up, and how quickly it disappears at any gathering.

Unbelievably Moist Texture: Thanks to the mayonnaise, this cake stays ultra moist and tender—even days after baking.
Rich Chocolate Flavor: The combination of cocoa powder and melted dark chocolate in the frosting makes every bite intensely chocolaty.
Simple to Make: Don’t let the fancy taste fool you—it’s straightforward, with common ingredients you probably already have.
Perfect for Any Occasion: Whether it’s a casual family dessert or a celebration, this sheet cake always steals the spotlight.

Ingredients & Why They Work

Each ingredient in this Decadent Chocolate Mayonnaise Sheet Cake Recipe is carefully chosen to balance flavor, texture, and moisture. Here’s a little insight into what makes them shine together—and some tips for shopping smart.

Flat lay of a small pat of fresh unsalted butter, a neat pile of all-purpose flour, a mound of rich unsweetened Dutch processed cocoa powder, a small heap of light brown sugar, a small heap of white granulated sugar, two large whole brown eggs with clean shells, a modest scoop of creamy mayonnaise, a small white bowl filled with hot dark coffee dissolved with instant espresso powder, a small white bowl of pure vanilla extract, a small white bowl of finely chopped bittersweet chocolate, a small white bowl of heavy cream, and a small white bowl of powdered sugar, all arranged in perfect symmetry on a clean white ceramic surface, placed on a clean white marble surface, soft natural light, photo taken with an iPhone, professional food photography style, fresh ingredients, white ceramic bowls, no bottles, no duplicates, no utensils, no packaging --ar 2:3 --v 7 --p m7354615311229779997

All-purpose flour: Provides structure—don’t swap for cake flour here, as the balance with cocoa and mayonnaise is precise.
Dutch processed cocoa powder: Gives a deep and smooth chocolate flavor without bitterness.
Baking powder & baking soda: Work together to give your cake the perfect rise and fluffy crumb.
Instant coffee powder: Enhances the chocolate flavor without a coffee taste—don’t skip this even if you’re not a coffee fan!
Eggs: Bind everything together and add richness.
Sugar (white and brown): The white sugar sweetens, while brown sugar adds subtle molasses notes and chewiness.
Mayonnaise: The secret weapon—adds moisture, keeps the cake tender, and blends right into the batter without a mayonnaise taste.
Vanilla extract: Lifts the chocolate and adds a mild sweet aroma.
Butter (for greasing): Prevents sticking and adds a tiny bit of richness to the cake edges.

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Note: You'll find the complete list of ingredients, along with their exact measurements, in the printable recipe card at the bottom of this post.

Make It Your Way

Sometimes I like to tweak this recipe based on the occasion or what I have on hand—don’t hesitate to make it yours! Adding your favorite mix-ins or swapping the frosting type can make it a unique treat every time.

Variation: I’ve added a handful of chopped walnuts or chocolate chips into the batter for extra texture—totally delicious!
Dietary modification: You can try using a vegan mayonnaise and substituting eggs with flax eggs for a dairy-free or vegan-friendly version.
Seasonal change: During the holidays, a pinch of cinnamon or chili powder in the batter gives a warm twist.

Step-by-Step: How I Make Decadent Chocolate Mayonnaise Sheet Cake Recipe

The image shows a single square piece of dark chocolate cake with two layers on a white plate with a thin gold rim. The bottom layer is thick and dark brown with a moist, rich texture, while the top layer is a thick, smooth milk chocolate frosting with a slightly wavy surface. A golden fork rests on the plate next to the cake. In the background, two more pieces of cake on white plates with gold rims are slightly out of focus, all set on a white marbled textured surface. Photo taken with an iphone --ar 2:3 --v 7

Step 1: Prep and Mix Dry Ingredients

Start by preheating your oven to 350°F (180°C) and greasing your 9x13-inch baking pan with butter to keep the cake from sticking. In a medium bowl, whisk together the all-purpose flour, Dutch processed cocoa powder, baking powder, baking soda, and salt to make sure everything is evenly combined. This helps your cake rise evenly and have an even crumb texture.

Step 2: Dissolve Coffee and Beat Mayonnaise with Sugars

In a glass measuring cup, stir your instant coffee powder into the hot water until fully dissolved—this really makes the chocolate pop. In a large mixing bowl, beat together the mayonnaise with both white and brown sugars until the mixture looks pale and creamy. This step might surprise you, but it’s key for a tender and sweet cake base.

Step 3: Add Eggs and Vanilla, Then Combine Wet and Dry Ingredients

Add the eggs one at a time into the mayonnaise-sugar mixture, beating well after each addition. Don’t forget to scrape down the sides to make sure everything mixes properly. Then pour in the vanilla extract. Now, gradually combine your dry ingredients and coffee with the wet mix, doing it in thirds—first third of flour mix with half the coffee, then the next third with the rest, and finally the last third of dry ingredients. The batter should be smooth, somewhere between thick and runny.

Step 4: Bake and Cool

Pour your batter evenly into the prepared baking pan and slide it into the oven. It should bake for about 28 to 30 minutes. Keep an eye on it after 25 minutes and use a toothpick to test—you're looking for moist crumbs clinging to it, not wet batter. Once done, remove the cake and allow it to cool completely in the pan before frosting. Trust me, frosting a warm cake is a recipe for a meltdown (literally!).

Step 5: Make the Rich Chocolate Frosting

Microwave the chopped dark chocolate in short bursts of 20 seconds, stirring in between, until completely melted and smooth. Let it cool a bit so it doesn’t melt your frosting ingredients. In another bowl, beat the butter until fluffy, gradually add powdered sugar, and beat on high for 2-3 minutes. Mix in the cocoa powder, scraping the bowl sides. Finally, pour in the heavy cream and melted chocolate, beating until everything is beautifully combined.

Step 6: Frost and Enjoy!

Spread the luscious frosting over the completely cooled cake using a spatula or the back of a spoon—you can get artistic here by making swirls or peaks. Slice it up, serve, and watch how quickly this cake disappears. Don’t forget to store leftovers in an airtight container—room temperature is fine for a day, or refrigerated for up to a week (frosted cake lasts around 3 days).

Top Tip

After making the Decadent Chocolate Mayonnaise Sheet Cake Recipe several times, I’ve picked up a few tricks to ensure perfect results every time—these little insights make all the difference between a good cake and an unforgettable one.

Gentle Folding: When combining wet and dry ingredients, mix just until combined to avoid a tough cake.
Cool Your Chocolate: Always let your melted chocolate cool slightly before adding it to the frosting to prevent it from seizing or thinning out.
Room Temperature Ingredients: Eggs and mayonnaise at room temperature incorporate better, yielding a smoother batter.
Don’t Rush Cooling: Be patient—frosting a warm cake can cause you frustration and a glazed mess.

How to Serve Decadent Chocolate Mayonnaise Sheet Cake Recipe

Chocolate Mayonnaise Cake - Serving Suggestion

Garnishes

I love topping this cake with simple extra touches like a sprinkle of flaky sea salt or some toasted pecans for a delightful crunch. A dusting of powdered sugar or a few fresh raspberries can add a beautiful pop of color and freshness that balances the richness.

Side Dishes

A scoop of vanilla bean ice cream or a dollop of whipped cream pairs impeccably with this chocolate cake. Sometimes, I serve it alongside fresh fruit salad to lighten things up—a perfect combo of indulgence and brightness.

Creative Ways to Present

For parties, I’ve cut this sheet cake into bite-sized squares and dusted them with cocoa powder or topped each piece with a mini chocolate shard. Adding edible gold flakes or chocolate curls can make it look fancy for special occasions—everyone thinks you spent hours perfecting it!

Make Ahead and Storage

Storing Leftovers

I usually leave the unfrosted cake in the pan, covered tightly with plastic wrap, at room temperature for a day—it holds up wonderfully. For longer storage, refrigerating it extends freshness up to a week. Just bring it back to room temp before frosting or serving for best texture.

Freezing

This cake freezes great! After baking and cooling, wrap the whole pan tightly in plastic wrap and foil, then freeze up to 3 months. Thaw overnight in the fridge and frost the next day for a fresh-baked taste whenever you want.

Reheating

If you have refrigerated slices left, I like to bring them to room temperature first. You can warm them gently in a microwave for 10–15 seconds, but don’t overdo it or the frosting melts too much. This way, each bite is as luscious as the first time.

Frequently Asked Questions:

Does the mayonnaise taste in the Decadent Chocolate Mayonnaise Sheet Cake Recipe?

Not at all! Mayonnaise is made of oil, eggs, and vinegar or lemon juice, which blend seamlessly into the batter. It acts as a moisture enhancer without imparting any mayo flavor—so you only get rich, tender chocolate cake.

Can I substitute the instant coffee powder in the recipe?

You can skip the instant coffee powder and just use hot water instead, but the coffee really brightens and deepens the chocolate flavor. If you don’t have instant coffee, instant espresso powder works great as a substitute. Avoid adding brewed coffee as it may affect batter consistency.

Why does this recipe use both baking powder and baking soda?

Using both creates the perfect rise and texture. Baking soda reacts with the acidic mayonnaise to help the cake rise. Baking powder also helps leaven the cake, ensuring it’s light and fluffy rather than dense. Together, they balance the chemistry perfectly.

Can I make this Decadent Chocolate Mayonnaise Sheet Cake Recipe gluten-free?

Yes! You can swap the all-purpose flour for a gluten-free baking blend that’s a 1:1 substitute. Just be sure to choose one with xanthan gum or a similar binder for structure. The mayonnaise helps with moisture, so it adapts well to gluten-free versions too.

Final Thoughts

This Decadent Chocolate Mayonnaise Sheet Cake Recipe holds a special place in my heart—not just for its amazing taste but because it’s a dessert that always brings people together with smiles and second helpings. I genuinely hope you’ll enjoy making it as much as I enjoy sharing it with you. Give it a try on your next cozy afternoon or special celebration—you might just find a new favorite.