Chocolate Sheet Cake with Candied Walnuts

chocolate sheet cake

This post is sponsored by California Walnuts. As always, all opinions are my own. 

I’m a fan of cake, of course, and while I’ve made plenty of layer cakes and snack cakes on this site, I realized that I could also do with a sheet cake, an essential for birthday parties, picnics, and other large get-togethers. This one is double chocolate, with sides coated in candied walnuts. 

I’ve teamed up with California Walnuts to bring you some recipes over the past year (such as this walnut snack cake with raspberry buttercream and  these raised donuts with chocolate glaze and candied walnuts). Over 99 percent of walnuts grown in the U.S. come from California’s walnut orchards, many of which are on family owned and operated farms that have been around for generations. Walnuts are nutritious and heart-healthy*, and offer 4 grams of protein and 2 grams of fiber per ounce. Walnuts are also the only nut with a significant amount of plant-based omega 3 ALA (2.5 grams/ounce). You can check out the CA Walnuts website for more nutrition info, research, tips for cooking with walnuts, and recipes. I’m excited to share more recipes with you!

chocolate sheet cake

chocolate sheet cake

chocolate sheet cake

chocolate sheet cake

Chocolate Sheet Cake with Candied Walnuts

A few notes: This cake has a higher ‘cake-to-frosting’ ratio, which is how my family prefers things. You can trim an inch off the cake (horizontally) if you want the cake portion to be shorter – just make sure the unfrosted cake is very cold (preferably frozen) when doing this, as the cake is tender. You could also bake the cake in two 8 x 2-inch square pans (divide the batter evenly between them), and then put the cakes right next to each other and frost. The frosting can be doubled if you want a more substantial layer. 


3 ounces (85g) bittersweet chocolate
1 cup hot coffee (hot water works, too)
1/2 cup sour cream
1/2 cup whole milk
1/2 cup canola oil
3 large eggs, room temperature
1 teaspoon pure vanilla extract
2 cups (284g) all-purpose flour
2 cups (396g) granulated sugar
3/4 cup (75g) Dutch process cocoa powder
2 teaspoons baking soda
1 teaspoon baking powder
1 teaspoon salt

Chocolate Buttercream
8 ounces (226g) semisweet chocolate, chopped
1 1/2 cups (339g | 3 sticks) unsalted butter, room temperature
1 teaspoon pure vanilla extract
2 tablespoons corn syrup
1/4 teaspoon salt
2 cups (226g) confectioners’ sugar
Sprinkles, if desired

Candied Walnuts
2 cups (200g) walnuts
1/2 cup (99g) granulated sugar
1/4 teaspoon salt

For the cake
Adjust an oven rack to the middle position. Preheat the oven to 350F. Butter and flour a 9 by 13-inch pan and line the bottom with parchment paper.

Put the bittersweet chocolate in a small bowl. Pour the hot water over it and cover with a piece of plastic wrap. In a medium bowl or liquid measuring cup, whisk the sour cream, milk, canola oil, eggs, and vanilla.

In the bowl of a stand mixer fitted with a paddle, mix the flour, sugar, cocoa powder, baking soda, baking powder, and salt on low until combined. With the mixer running on low, slowly add the sour cream mixture. Increase the speed to medium and beat until combined, 20 to 30 seconds.

Whisk the chocolate and hot water together until completely smooth. With the mixer running on low, slowly pour the chocolate mixture into the batter and mix until just combined. Using a spatula, give the batter a couple of turns to make sure it is fully mixed.

Pour the batter evenly into the prepared pans. Bake 25 to 35 minutes, until a wooden skewer or toothpick comes out with the tiniest bit of crumb.

Transfer the cakes to a wire rack and let cool for 30 minutes. Turn the cakes out onto a half sheet pan lined with parchment paper, remove the parchment paper from the bottom of the cakes, and let the cakes cool completely upside-down (this will help deflate any doming). Once cool, the cakes can be wrapped in plastic and refrigerated overnight or frosted (cake can also be frozen unfrosted for up to one month).

For the buttercream
Put about 1 inch of water in a medium saucepan and bring it to a gentle boil.

Melt the chocolate in a heatproof bowl set over the pan of boiling water, being careful not to let the water touch the bottom of the bowl. Stir constantly until just melted and set aside to cool slightly.

In the bowl of stand mixer fitted with a paddle, beat the butter on medium until light yellow and fluffy, about 3 minutes. Add the vanilla, corn syrup, and salt and beat on medium until combined. Turn the mixer to low and gradually add the confectioners’ sugar. Beat at medium, stopping to scrape down the sides of the bowl as necessary, until smooth and creamy, 2-3 minutes. Add the chocolate and mix on low speed until no streaks remain.

For the candied walnuts
In a large skillet, stir together the walnuts, sugar and salt. Cook over medium heat until the sugar begins to melt and the nuts begin to toast, stirring almost constantly. Once the sugar begins to melt, turn the heat down to low and cook until the nuts are lightly caramelized. Pour the nuts onto baking sheet lined with parchment paper. Let them cool completely before chopping into small pieces. 

To assemble
Frost the cake with the chocolate buttercream. Press the chopped, candied walnuts into the sides of the cake, then decorate with sprinkles if desired. 

chocolate sheet cake

*Supportive but not conclusive research shows that eating 1.5 ounces of walnuts per day, as part of a low saturated fat and low cholesterol diet, and not resulting in increased caloric intake may reduce the risk of coronary heart disease. One ounce of walnuts provides 18g of total fat, 2.5g of monounsaturated fat, 13g of polyunsaturated fat, including 2.5g of alpha-linolenic acid, the plant-based omega-3.

  • Reply
    cheryl nobuta
    Saturday, April 4, 2020 at 12:41 pm

    Made this last night and it was the best chocolate cake I have ever made! My husband and I practically ate half of it lol. I didn’t have walnuts so had to skip that but will definitely make it again with the candied walnuts. The recipe does make quite a bit of buttercream, probably would make only half next time. Another adjustment I had to make was buttermilk for whole milk. The crumb was delicious and the best texture.
    Thanks for sharing Sarah!

  • Reply
    Thursday, December 19, 2019 at 12:25 am

    I really love chocolate cake. This cake may be on everyone’s favorite list of cake. Thank you so much for sharing “YUMMY” delightful recipe. Keep it up!

  • Reply
    Sunday, November 24, 2019 at 8:25 am

    Yum! I’m drooling over this amazing recipe! This is visually striking! I’d love to give this cake a try and share with my family and friends. I’ll probably make this for my friend’s birthday next weekend. Gonna follow your recipe precisely.
    Thank you for sharing this idea and inspiring me. All of your useful tips will surely help me and your readers a lot. I’m so happy to have stumbled across your awesome blog. My day wasn’t a total loss. Look forward to your new ideas. I really appreciate all of your hard work and effort. Keep it up!

  • Reply
    Wednesday, September 25, 2019 at 2:24 pm

    An ideal recipe to consider for promoting the use of walnuts is Hungarian Nut Roll (Potica). Yum!

  • Reply
    Kathrin |
    Tuesday, September 17, 2019 at 9:37 am

    Really an awesome recipe I’d love to try – This goes straight to my cake recipe list 🙂

  • Reply
    B?t Cacao Nguyên Ch?t
    Monday, September 16, 2019 at 3:49 am

    OMG!! I wanna try this asap!!

  • Reply
    Tuesday, September 10, 2019 at 6:37 am

    Helpful one! Thank You so much.

  • Reply
    Sunday, September 8, 2019 at 12:22 am

    This looks delicious! Are either the cake or the frosting sensitive to the cacao percentage in the chocolate? Thanks!

  • Reply
    Saturday, September 7, 2019 at 10:24 am

    Dying over these drool-worthy photos, Sarah. Love!

  • Reply
    Saturday, August 31, 2019 at 11:54 am

    I love sheet cakes! This chocolate sheet cake looks so delicious and perfect for the weekend ?

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