Chocolate Mayonnaise Cake | Easy Moist Chocolate Sheet Cake Recipe

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This incredibly moist and rich chocolate mayonnaise cake is adapted from Jill O’Connor’s wonderful cookbook, Cake, I Love You. You’re going to love the ease of this chocolate sheet cake recipe and the texture and chew of the rocky road frosting!

If you’re not a fan of rocky road, you can leave out the marshmallows and nuts and enjoy this chocolate sheet cake “straight.” Use the melted chocolate bar frosting Jill created, because it is fantastic.

You can also go with your favorite frosting for chocolate cake such as American buttercream frosting or ermine frosting (my favorite). And don’t miss the mint version, mint chocolate sheetcake. It’s a wonderful variation on a traditional chocolate mayonnaise cake!

Chocolate Sheet Cake Video

I’ve put together a little video for you to walk you through making this cake. I hope you find it helpful. I also go into great detail about how to make this cake and troubleshooting any issues in the post itself. Please refer to the Table of Contents.

Cake, I Love You

Jill O’Connor is one of my favorite people in the world. Not only does she write swoony cookbooks and a column for the San Diego Union-Tribune AND give talks to the Culinary Historians of San Diego AND appear on Home & Family, she is also Very, Very hilarious and a wonderful person.

I love her. And I love cake. So when Jill’s most recent book, Cake, I Love You, came out (it’s now celebrating its first birthday!), I needed to own it and bake from it.

This chocolate sheet cake is a spin I put on her wonderful Chocolate Mayonnaise Cake with Melted Chocolate Bar Frosting from Cake, I Love You.

There are no melted chocolate bars in the recipe, but the frosting does taste quite like a melted candy bar. Luscious, rich, and shiny. Perfect. So of course the Rocky Roadness is just gilding the lily.

If you are a fan of gilded lilies, you’ll want to try my version with toasted, chopped nuts and mini marshmallows.

You can watch Jill demonstrate how to make her Old-Fashioned Chocolate Mayonnaise Cake with Melted Candy Bar Frosting on Home & Family.

A Little Mayonnaise Cake History

Much like old-fashioned pie recipes or “desperation pies” (Lord, we’re out of fruit, and I need pie. Let’s see what’s in the cupboard), mayonnaise cake was born of the desperation of Depression Era in the United States.

Butter was hard to come by, so ingenious bakers subbed in mayonnaise, which is pretty much just oil with a little egg, some vinegar, and salt.

Even mayonnaise companies jumped on the mayo cake bandwagon and started printing the recipe right on the jar. Today, Hellman’s has a very fine chocolate mayonnaise recipe printed on their website.

PRO TIP: Check the salt level of the mayonnaise you are planning to use. If your mayonnaise is pretty salty, you may have to add minimal, if any, additional salt.

Let your palate be your guide, and know that chocolate mayonnaise cake is incredibly moist, delicious, and easy to make.

How To Make Chocolate Mayonnaise Cake

Step by Step Photos, Tips, Tricks, and Troubleshooting

Ingredients and Mixing Method

1. Scale out your dry ingredients. You will want a kitchen scale for this. Trust me–it makes your life much easier. Weigh the flour and cocoa powder. You can use measuring spoons to measure the small amounts of salt and leavening.
2. Sift together your dry ingredients. I like to use a regular mesh strainer for this. No need to buy a dedicated sifter unless you really want one. I sifted the ingredients together twice to get them fairly evenly combined.
3. Weigh out your sugar. For the rest, a liquid measure will do just fine for the water. You’ll also need 2 eggs, vanilla, and instant coffee or espresso powder.
4. And the secret ingredient to keep things moist and wonderful: mayonnaise!

1. Place sugar and eggs in the bowl of your stand mixer. (You can also use a hand mixer with no problem.) Fit it with the paddle attachment and beat on medium high speed for about 5 minutes.
2. You’re looking for the ribbon stage. The mixture will be light in color and relatively thick. See how it looks when it falls off the beater? Ribbon. Because you’re using a fair amount of sugar and relatively little liquid (in the egg whites), not all the sugar will be dissolved at this point. That’s okay.
3. Beat in the mayo and vanilla until smooth.
4. Alternate adding the sifted dry ingredients with the hot water/instant coffee or espresso powder. Add about 1/3 of the dry followed by half the wet, half of the remaining dry, the rest of the wet, and end with dry. Be sure to scrape down around the sides and the bottom of the bowl with a large, flexible silicone spatula a couple of times during these additions to keep the mixture uniform.

Baking the Mayonnaise Cake

The next collage doesn’t show steps, but it does show the texture of the batter and what you’re looking for when the chocolate mayonnaise cake is fully baked.

Notice the baked cake is no longer shiny, is well-risen, and pulls away from the sides of the pan just slightly. I shoot for an internal temperature of 195F to 200F, and yes, I check the temperature with an instant read thermometer.

Making the Rocky Road Frosting

The frosting is easy to make, and as a bonus, you don’t need a mixer at all.

1. Put the milk and dark chocolate chips, along with the stick of butter, in a microwave-safe bowl.
2. Melt in bursts and then stir until completely smooth.
3. Whisk in room temperature sour cream.
4. Keep whisking until the mixture is smooth.

1. Sift the powdered sugar into the frosting.
2. Whisk until smooth.
3. Fold in about 2/3 of your marshmallows and chopped nuts.

To Frost the Chocolate Sheet Cake

1. Spread half the frosting on the cake.
2. Scatter the reserved mini marshmallows and chopped nuts evenly over the cake.
3. Add the rest of the frosting in “blobs” evenly spaced over the mallows and nuts.
4. Spread/swirl. You want some mallows and nuts to still be showing.

NOTE: Store the cake in the refrigerator. It’ll help firm up the frosting a bit and make the cake easier to slice. Slice the cake while chilled, but let the slices sit out for about 30-45 minutes before serving so they come back to room temperature.

Tips, Tricks, Troubleshooting

This is a pretty straightforward cake to make. You don’t have to make homemade marshmallows. If you’d like to, though, here is the recipe for the mallows. Rather than spreading in a round pan, I spread the mallow mixture onto a prepared half sheet pan.

If you’d like the frosting to be a bit thicker (especially if you plan on leaving out the rocky road part), beat with a hand mixer or stand mixer.

This will incorporate some air, lighten the texture to make it easier to spread, and give you the perfect slice of chocolate sheet cake.

As easy as this cake is to make, you could potentially run into some issues. I’ll try to answer any questions you have before you get started. If you have other questions, please don’t hesitate to email me or leave a comment on this post.

Chocolate Mayonnaise Cake, Q&A

• Should I use Dutch process cocoa to make this cake? No. Use American-style cocoa powder. It’s lighter and more red in color than Dutch process or alkalized cocoa powder. Dutch process means that the cocoa powder has been treated with an alkali to neutralize the pH. American style cocoa powder is slightly acidic, and the baking soda is in the recipe to neutralize it. If you use Dutch process cocoa and keep the baking soda, your cake will taste a bit soapy, which is no good at all.
• I don’t have instant coffee or espresso powder, and I don’t want to order it. What can I use instead? No problem. Just use hot brewed coffee, and you’ll be fine.
• Can I substitute sour cream for the mayonnaise? No. Sour cream is mainly dairy, and mayonnaise is mainly oil. You will not get good results using sour cream–there is not enough fat in it to make the cake nice and moist.
• Can I use a hand mixer to make this cake? You can, but your results might not be quite as good. You really need the power of a stand mixer to achieve a nice ribbon stage in the step where you beat the sugar and eggs together. You can’t really achieve the desired result with a hand mixer.
• What kind of nuts should I use in the rocky road frosting? And can I leave them out if I don’t like nuts? I used a combination of chopped chocolate covered cashews and toasted almonds. You can use whatever nuts you prefer. Hazelnuts, pecans, or peanuts would work nicely too. And you can use a mixture of your favorite nuts as well. You don’t have to add nuts or marshmallows to the frosting at all. Jill’s original recipe contains neither marshmallows or nuts, so it’s totally your call.
• Can I make this into a layer cake? Yes! Jill’s original recipe gives directions for making this cake in round pans.
  • Spray your cake pans and line the bottoms with parchment rounds
  • Divide the batter evenly between the two pans, and bake for 20-25 minutes.
• Is the cake hard to slice with all those nuts in it? I would probably not make the rocky road frosting if making a layer cake. The cake is hard to slice cleanly when you hit a nut, so having nuts both in the filling between the layers, around the side, and on the top is a recipe for a very messy slicing experience. If you still want to make the rocky road frosting, I’d slice the cake first and then just add the mallows and chopped nuts to the top of each slice.

More Cake Recipes to Enjoy

If you are looking for more cake recipes, I can help. Try these great cakes on for size!

• Lemon Corn Buttermilk Pound Cake
• Fudgy Black Forest Cake
• Chocolate Espresso Pound Cake

And don’t forget to take a look at Jill’s wonderful Cake, I Love You.

Let’s Make This Chocolate Cake, Y’all

If you like the sound of this recipe, please rate it and/or leave a comment for me. I love hearing from you! And if you make this recipe, please share a photo! Tag me on Instagram at @onlinepastrychef with hashtag #pcorecipe!

Pin for Later

And there you have it, a rich, moist, and crowd-pleasing old-fashioned chocolate mayonnaise cake. Make it with my rocky road frosting or leave out the mallows and nuts to stay true to Jill’s original recipe. Either way, you’re going to love this cake. I promise.

Thanks for spending some time with me today. And I really do love hearing from you, so please leave a comment, rate the recipe, and/or ask a question. I’m happy to help.

Take care, and have a lovely day.

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