This chocolate zucchini cake is even more moist than my Homemade Ultra Moist Chocolate Cake, which I didn’t think was possible. It hides three cups of shredded zucchini under a thick layer of chocolate frosting, and nobody can tell because the zucchini melts into the cake as it bakes.
I make a birthday cake for everyone in my family every year, and whoever’s birthday it is picks the cake. My dad loves chocolate, so he always gets a chocolate cake.
This year, a friend dropped off more zucchini than usual, and everyone in my pottery class loved the Fudgy Zucchini Brownies I’d made a week or so earlier. I decided to bake my dad a zucchini cake to see if he’d even notice, because I’m mean like that.
Spoiler alert, he didn’t notice! He probably wouldn’t have touched it if I’d told him first, but he loved it and went back for a second slice after I told him.
I’ve made it twice since then. I usually bake it in a 9×13 pan because it’s so much easier, but it also works as a layer cake.
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Mayo Makes This Cake Extra Moist
The secret ingredient is a third cup of real mayonnaise. It makes the cake rich and moist without making it heavy, and no, it doesn’t taste like mayo.
If you’re from Chicago or know Portillo’s, you’ve probably heard everyone say mayo is the secret ingredient in their chocolate cake, so this isn’t some weird, wacky thing I made up. Use any brand of real mayo you like since you can’t taste it, but skip salad dressing like Miracle Whip.
Mayo is mostly oil and egg, and the batter already has both. That’s why it adds richness without any odd flavor.
Why Add Coffee
Coffee deepens chocolate flavor, so a little in the batter makes this cake taste more chocolatey without tasting like coffee. I use two tablespoons of strong coffee, and leftover coffee from the pot works fine as long as it’s cooled.
If you don’t keep coffee on hand, dissolve one teaspoon of espresso powder in two tablespoons of warm water and use that instead. The frosting also gets a quarter teaspoon of espresso powder. It’s optional, but it makes a difference.
Why Add Cinnamon
I love the combination of cinnamon and zucchini, like in Zucchini Bread, and I also love the combination of chocolate and cinnamon, a classic Mexican flavor. Here, the cinnamon complements both ingredients, and I use enough that you can still taste a hint of cinnamon alongside the chocolate.
If you aren’t a cinnamon fan, you can use less than I do, but even my daughter, who swears she doesn’t like cinnamon, loves this cake as is. I would still use some cinnamon because it intensifies the other flavors, but you can reduce it to one teaspoon if you prefer.
How to Make Chocolate Zucchini Cake
Prep the Zucchini
Shred the zucchini first. I use my Microplane ribbon grater, but a box grater with small holes or a food processor with a grating attachment works, too. Pick out any seeds that make it through.
Put the shredded zucchini in a colander and let it drain while you make the batter, usually for about 20 to 30 minutes. Right before you add it, press out as much water as you can and pack it into a liquid measuring cup until you have three cups.
A liquid measuring cup makes it easy to see how much you have. I use the same one I measure the oil in, so it’s one less dirty dish to wash.
This grater works, and it’s easy to use. It’s lasted for well over a decade in my house. In addition to grating cheese, this works perfectly for coconut, chocolate, carrots, and more.
Make the Cake
Preheat the oven to 350 degrees and grease a 9×13 metal pan. Beat the oil and both sugars together in a stand mixer, then add the eggs one at a time along with the mayo, beating after each addition. A hand mixer works just as well, but I wouldn’t mix this one by hand.
Use room-temperature eggs so they blend into the oil and sugar smoothly. If I forget to set them out, I put them in a small bowl of warm water for about five minutes.
Add the cocoa, coffee, baking soda, baking powder, salt, and cinnamon, then mix on low until the cocoa is mostly combined so it doesn’t fly around the kitchen. Then beat it well.
Add the flour and stir just until most of the white streaks are gone. Last up, mix in the zucchini and chocolate chips to distribute them evenly.
Bake and Cool
Bake the cake for 50 to 55 minutes. Ovens and pans bake differently, so start checking at 50 minutes.
Look for cracks across the top, then poke a toothpick into the center. It should come out with a few moist crumbs but no wet batter.
If the toothpick comes out with glossy, melted chocolate instead of dull, wet batter, it hit a chocolate chip, so test another spot. Let the cake cool completely in the pan before frosting, which takes about an hour.
Make the Frosting
Make sure your butter is soft but nowhere near melted. Beat it on low with the cocoa powder and espresso powder until combined, then beat until light and fluffy.
Add the milk, vanilla, salt, and powdered sugar. Mix on the lowest speed until the powdered sugar is combined, or it’ll fly everywhere, then beat it on high for three to five minutes until it’s fluffy.
This ratio works for me, but you can add a little more milk to loosen it or more powdered sugar to thicken it. It makes a deliciously thick layer of frosting on a 9×13 cake.
Drop dollops of frosting all over the cooled cake, then smooth them together with an offset spatula. This method keeps the frosting from pulling at the cake, so you don’t end up with crumbs in your frosting.
This time, I started with my standard spatula, and it was awkward. Switching to that offset spatula really helped.
Can You Taste the Zucchini in Chocolate Cake
No. The zucchini adds moisture, and between the chocolate and the cinnamon, nobody can pick it out. If you have picky eaters, my Double Chocolate Zucchini Muffins are another easy way to sneak in zucchini.
Do You Peel Zucchini for Chocolate Zucchini Cake
No, I leave the skin on. The skin is thin, and the green flecks disappear in a cake this dark.
Can You Make Chocolate Zucchini Cake as a Layer Cake
Yes, and that’s how I made it for my dad’s birthday. Use two 9-inch round cake pans, line the bottoms with parchment paper, and then grease the parchment and the sides of the pans. Bake the rounds for 28 to 32 minutes.
Let the rounds cool in the pans for at least an hour before you turn them out. If you turn them out too soon, they’ll fall apart.
The frosting recipe isn’t enough to fill and frost a layer cake, so double it. The recipe notes list the exact amounts, and a layer cake yields 16 slices.
How Long Does Chocolate Zucchini Cake Last
Chocolate zucchini cake keeps on the counter for up to three days. Cover it with foil or a lid, and I love my 9×13 pan with a snap-on plastic lid for this.
This is my favorite 9×13 pan because the lid makes it easy to transport when I plan to share my treats. It also creates an easy and convenient way to store any leftovers because the lid just snaps on.
Eat it within three days, though. All that zucchini makes it so moist that it spoils faster than other cakes.
Can You Freeze Chocolate Zucchini Cake
I don’t freeze this cake, but you can. Freeze it uncovered for about an hour until the frosting is firm, then wrap it tightly in plastic wrap and freeze it for up to two months.
When you want some, cut off as many pieces as you need. Thaw them unwrapped on the counter so they don’t get soggy.
Chocolate Zucchini Cake
Ingredients
For the Cake
- 2 medium zucchini about 1 pound, shredded, to yield 3 cups packed after squeezing out the water
- 1 cup canola or vegetable oil
- 1 cup granulated sugar
- 3/4 cup packed light brown sugar
- 4 large eggs at room temperature
- 1/3 cup mayonnaise
- 3/4 cup unsweetened natural cocoa powder
- 2 tablespoons strong brewed coffee cooled
- 2 teaspoons baking soda
- 1/2 teaspoon baking powder
- 1/2 teaspoon salt
- 1 tablespoon ground cinnamon
- 2 cups all-purpose flour 250 grams
- 1 cup semi-sweet chocolate chips
For the Frosting
- 3/4 cup unsalted butter softened
- 7 tablespoons unsweetened cocoa powder
- 1/4 teaspoon espresso powder optional
- 2 tablespoons whole milk plus more as needed
- 1/2 teaspoon vanilla extract
- Pinch salt
- 2 cups powdered sugar
Instructions
- Preheat the oven to 350 degrees. Grease a 9×13 metal baking pan.
- Shred the zucchini with a ribbon grater, the small holes of a box grater, or a food processor with a grating attachment, and pick out any seeds. Put the zucchini in a colander to drain while you make the batter.2 medium zucchini
- In a bowl, beat the oil, granulated sugar, and brown sugar until combined.1 cup canola or vegetable oil, 1 cup granulated sugar, 3/4 cup packed light brown sugar
- Add the eggs one at a time, then the mayonnaise, beating after each addition.4 large eggs, 1/3 cup mayonnaise
- Add the cocoa powder, coffee, baking soda, baking powder, salt, and cinnamon. Mix on low until the cocoa is mostly combined, then beat well.3/4 cup unsweetened natural cocoa powder, 2 tablespoons strong brewed coffee, 2 teaspoons baking soda, 1/2 teaspoon baking powder, 1/2 teaspoon salt, 1 tablespoon ground cinnamon
- Add the flour and stir just until most of the white streaks are gone.2 cups all-purpose flour
- Press as much water as you can from the zucchini and pack it into a liquid measuring cup to measure 3 cups. Add the zucchini and chocolate chips to the batter and mix until combined.1 cup semi-sweet chocolate chips
- Spread the batter in the pan. Bake for 50 to 55 minutes, until the top has cracks and a toothpick in the center comes out with moist crumbs but no wet batter. Melted chocolate from a chip looks glossy, so if the toothpick lands in one, test another spot.
- Let the cake cool completely in the pan, about 1 hour.
- Beat the softened butter, cocoa powder, and espresso powder until light and fluffy.3/4 cup unsalted butter, 7 tablespoons unsweetened cocoa powder, 1/4 teaspoon espresso powder
- Add the milk, vanilla, salt, and powdered sugar. Mix on the lowest speed until the powdered sugar is combined.2 tablespoons whole milk, 1/2 teaspoon vanilla extract, Pinch salt, 2 cups powdered sugar
- Beat on high for 3 to 5 minutes until fluffy. Add more milk to loosen the frosting or more powdered sugar to thicken it.
- Drop dollops of frosting over the cooled cake and smooth them together with an offset spatula.
Notes
- To make this a layer cake, line the bottoms of two 9-inch round cake pans with parchment paper, then grease the parchment and the pans’ sides. Bake for 28 to 32 minutes. Cool the rounds in the pans for at least 1 hour before turning them out, or they can fall apart. Makes 16 slices.
- For layer cake frosting, double the frosting to fill and frost the layers. Use 1 1/2 cups unsalted butter, 3/4 cup cocoa powder plus 2 tablespoons, 1/2 teaspoon espresso powder, 1/4 cup milk or cream, 1 teaspoon vanilla, a pinch of salt, and 4 cups powdered sugar.
- If you don’t have coffee, dissolve 1 teaspoon espresso powder in 2 tablespoons warm water and use it in place of the brewed coffee.
- Room-temperature eggs blend in more smoothly. If yours are cold, set them in a bowl of warm water for about 5 minutes.
- Store the cake covered on the counter for up to 3 days. To freeze, chill it uncovered for about 1 hour until the frosting is firm, then wrap tightly in plastic wrap and freeze for up to 2 months. Thaw pieces unwrapped on the counter.
Nutrition
This site uses an online source to provide nutrition estimates as a courtesy. If you need exact values, please calculate yourself.
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