Name: 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

Nothing beats the rich, moist decadence of a chocolate cake that feels like a hug in dessert-form. That's why I adore this Chocolate Mayonnaise Sheet Cake Recipe—it’s incredibly tender and fudgy, thanks to a secret ingredient you wouldn’t expect: mayonnaise!

A glass tray holds a rich, dark brown cake with a thick, smooth layer of lighter brown frosting on top that has soft swirls and peaks. Three square pieces have been cut from the cake, showing the dense, moist texture of the dark cake underneath the glossy, creamy frosting. The cake sits on a white marbled surface with some crumbs around the tray edges. 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 Chocolate Mayonnaise Sheet Cake Recipe
Top Tip
How to Serve Chocolate Mayonnaise Sheet Cake Recipe
Make Ahead and Storage
Frequently Asked Questions:
Final Thoughts
Chocolate Mayonnaise Sheet Cake Recipe

Why You'll Love This Recipe

This Chocolate Mayonnaise Sheet Cake Recipe caught me by surprise the first time I made it—it’s so simple but produces this insanely moist and tender crumb that you won’t believe came from mayonnaise! It’s my go-to for big gatherings or when I want something fuss-free but spectacular.

Unexpected Moisture: Mayonnaise replaces butter and oil here for an ultra-moist, tender texture without any greasy feel.
Easy to Make: No complicated steps or fancy gadgets—perfect when you want a quick, crowd-pleasing dessert.
Rich Chocolate Flavor: Cocoa powder, a touch of instant coffee, and melty chocolate frosting deliver deep, intense chocolate notes.
Versatile Sheet Cake: Great for everyday treats, birthdays, or potlucks—you can dress it up or keep it simple.

Ingredients & Why They Work

This recipe uses some pantry staples but with a twist that makes all the difference. Combining Dutch-process cocoa with a splash of instant coffee brings out the chocolate’s depth, while mayonnaise adds moisture and richness without any egginess.

Flat lay of a small white ceramic bowl of all-purpose flour, a small white ceramic bowl of unsweetened Dutch processed cocoa powder, a small white ceramic bowl of light brown baking powder, a small white ceramic bowl of light brown baking soda, a small white ceramic bowl of coarse salt, a small white ceramic bowl of hot water with dissolved instant coffee powder, two large whole brown eggs with clean shells, a small white ceramic bowl of white granulated sugar, a small white ceramic bowl of packed brown sugar, a small white ceramic bowl of creamy mayonnaise, a small white ceramic bowl of amber vanilla extract, a small white ceramic bowl of finely chopped dark semisweet chocolate, a small white ceramic bowl of unsalted butter cubes, a small white ceramic bowl of powdered sugar, a small white ceramic bowl of heavy cream 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: The base for structure; I prefer gold-standard all-purpose to get just the right crumb.
Dutch-processed cocoa powder: Provides a smooth, bold chocolate flavor without acidity.
Baking powder & baking soda: These leaveners ensure a light rise and tender cake.
Salt: Just a pinch balances and enhances the chocolate flavors.
Hot water & instant coffee powder: The coffee isn’t for flavoring coffee lovers necessarily—it just amplifies the chocolate notes, making the cake taste richer.
Eggs: Bind everything together and add a little structure.
Sugar & brown sugar: The combo balances sweetness and moisture while giving a subtle caramel undertone from the brown sugar.
Mayonnaise: The star secret! It’s mostly eggs and oil, so it strengthens and moistens the cake beautifully without making it greasy.
Vanilla extract: Just a touch lifts all the flavors harmoniously.
Semisweet or bittersweet chocolate: Melted into the frosting for richness and that glossy finish.
Unsalted butter: Creams into the frosting for smoothness and flavor control.
Powdered sugar: Sweetens and gives the frosting a smooth, silky texture.
Heavy cream: Adds softness and makes the frosting irresistibly creamy.

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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

I’ve played around with this Chocolate Mayonnaise Sheet Cake Recipe quite a bit, and honestly, it’s fantastic on its own. But if you’re feeling adventurous, customizing it is half the fun — and it’s forgiving to tweaks!

Variation: Adding a handful of chocolate chips to the batter ups the fudginess—I've done this for family movie nights, and everyone loved the surprise pockets of melty chocolate.
Dairy-Free Version: You can swap the butter in the frosting for a dairy-free margarine and use a plant-based mayonnaise for allergy-friendly tweaks.
Seasonal Flair: Try stirring in a pinch of cinnamon or espresso powder in the frosting for a cozy fall twist.
Less Sweet: If you prefer less sugar, I recommend cutting back the powdered sugar in the frosting by about ¼ cup.

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

A thick slice of dark chocolate cake with two layers is placed in the center of a round white plate with a gold rim. The bottom layer is a dense, moist dark brown cake with a rough texture, while the top layer is a smooth and creamy light brown chocolate frosting, spread unevenly with some soft peaks. A shiny gold fork rests diagonally on the lower left side of the plate. In the blurred background, two more slices of the same cake on white plates with gold rims sit on a white marbled surface, creating a cozy dessert setting. photo taken with an iphone --ar 2:3 --v 7

Step 1: Prep Your Pan and Dry Ingredients

Start by brushing a 9x13-inch baking pan lightly with butter—this helps the cake release easily after baking. Then, whisk together your flour, cocoa, baking powder, baking soda, and salt in a medium bowl until the mixture looks uniform and smooth. This even distribution is key for consistent rising and flavor.

Step 2: Mix Coffee and Beat Mayo with Sugars

In a separate jug, dissolve the instant coffee powder in hot water to unlock those chocolate-enhancing flavors. Then, grab a large bowl and beat the mayonnaise with the white and brown sugars until the mix turns pale and creamy. This lightening of color means air is incorporated, which helps the cake’s texture.

Step 3: Blend in Eggs and Vanilla

Add eggs one at a time, beating well after each addition to make sure they fully mix in without curdling. Don’t forget to scrape down the sides of your bowl every now and then—trust me, this little tip keeps the batter smooth and ensures nothing gets left behind. Then whisk in the vanilla extract.

Step 4: Combine Wet and Dry Ingredients with Coffee

Now comes the fun part—you’ll add your dry ingredients and coffee in thirds. Stir in the first third of the flour mixture along with half the coffee, mix until combined, then repeat for the second batch. After adding the last third of dry mix, give it one last stir. The batter should feel smooth—think thick but pourable, not stiff or runny.

Step 5: Bake and Cool

Pour the batter evenly into your prepared pan, smooth it out gently, and bake at 350°F (180°C) for about 28 to 30 minutes. Don’t skip the toothpick test—when inserted, it should come out with moist crumbs clingy to it, not raw batter. Let it cool completely before frosting—patience here pays off!

Step 6: Create the Decadent Chocolate Frosting

Melt your chopped chocolate in short bursts in the microwave, stirring between intervals until glossy and smooth—cool it a bit so it doesn’t melt the frosting later. Then beat your butter until it’s fluffy before slowly adding powdered sugar and cocoa powder, mixing well. Finish by beating in cream and the cooled chocolate; chill the frosting for 10 minutes so it firms up nicely for spreading.

Step 7: Frost and Serve!

Spread that luscious frosting over the cooled cake with a spatula, swirling it around for a rustic, inviting look. Cut into squares, serve, and watch your guests swoon. If you like, store it covered at room temp for a day or refrigerate up to a week; just bring to room temp before slicing for the best frosting texture.

Top Tip

From baking this cake multiple times, I’ve gathered a few insider tricks that really make the difference between just good and absolutely wonderful.

Room Temperature Ingredients: I always bring my eggs and mayonnaise to room temp before mixing—they blend smoother and help prevent a lumpy batter.
Don’t Overmix After Adding Flour: Fold the dry ingredients just until combined. Overmixing can make the cake tough.
Let the Cake Cool Fully: Frosting a warm cake will cause the frosting to melt and slide off. Give it at least 30 minutes to cool completely.
Let Frosting Rest Before Using: Cooling the frosting in the fridge for about 10 minutes firms it up just enough to spread easily without sliding.

How to Serve Chocolate Mayonnaise Sheet Cake Recipe

chocolate mayonnaise cake - Serving Suggestion

Garnishes

I love keeping it classic with a dusting of cocoa powder or some extra chocolate shavings on top. Another favorite is sprinkling chopped toasted pecans or walnuts for a bit of crunch and nutty richness that contrasts perfectly with the creamy frosting.

Side Dishes

Since this cake is wonderfully rich and moist, I like pairing it with fresh berries or a scoop of vanilla bean ice cream to balance the chocolate decadence with refreshing brightness. A simple cup of coffee or milk also complements the richness perfectly.

Creative Ways to Present

For birthdays, I’ve layered this sheet cake with whipped cream and fresh raspberries in the middle for an unexpected twist. Or, you can cut it into smaller squares and serve as bite-sized treats on a dessert platter—perfect for parties where everyone wants a taste without the guilt.

Make Ahead and Storage

Storing Leftovers

After baking, leave the cake in the pan and cover it tightly with plastic wrap. It keeps beautifully at room temperature for about a day or you can refrigerate it for up to a week. Once frosted, store it in the fridge for up to three days, but remember to let it warm to room temperature before slicing so the frosting softens.

Freezing

I’ve frozen this cake both frosted and unfrosted. When unfrosted, wrap tightly in plastic wrap and foil, then freeze up to 3 months. Thaw overnight in the fridge before frosting. Freezing with frosting is trickier—wrap carefully and thaw slowly to avoid condensation ruining the texture.

Reheating

If you want to warm a slice, I use a microwave for about 15 seconds—it brings out that melty, almost brownie-like texture I adore. Just avoid overheating or the frosting can get too soft and messy.

Frequently Asked Questions:

Why mayonnaise in a chocolate cake?

Mayonnaise is mostly made of eggs and oil, so it replaces butter or oil in the recipe while adding extra moisture and richness. It keeps the cake tender and helps achieve a moist crumb without greasiness.

Can I substitute regular cocoa for Dutch-processed cocoa?

You can use regular cocoa powder, but Dutch-processed cocoa provides a smoother, less acidic flavor and gives the cake a deeper color and richer taste. If you replace it with natural cocoa, consider adding a little extra baking soda to balance acidity.

Do I have to use coffee in the recipe?

The instant coffee or espresso powder enhances the chocolate flavor but doesn’t make the cake taste like coffee. If you prefer, you can leave it out—but I recommend at least a teaspoon to boost the chocolate depth.

How do I store leftover frosted cake?

Store leftover frosted cake covered in the refrigerator for up to 3 days. Let it come to room temperature before serving to soften the frosting and improve texture. Ensure it’s tightly wrapped to keep it from drying out.

Final Thoughts

This Chocolate Mayonnaise Sheet Cake Recipe holds a special place in my baking repertoire because it’s consistently astonishing how a common kitchen staple like mayo can turn an ordinary chocolate cake into something so moist, tender, and flavorful. Whether you’re making it for your family or a crowd, it delivers every time—and I can’t wait for you to experience that moment when you first bite into this fabulously fudgy, luscious sheet cake. Give it a try—you’ll want to make it again and again!