Sweet Potato Layer Cake with Marshmallow Frosting

Move over Thanksgiving turkey, this Sweet Potato Layer Cake will be this year’s show stopping centerpiece. Layers of moist, gently spiced sweet potato cake are surrounded by swirls of marshmallow frosting for a mouthwatering masterpiece that tastes as epic as it looks.

Whether you love it or hate it, sweet potato casserole has been a feature of the Thanksgiving dinner spread here in the US for generations. We’re all familiar with some kind of variation whether your mom made it with canned candied yams and mini marshmallows or fresh sweet potatoes topped with a toasted marshmallow crumble. This year I’m skipping the controversial casserole and trading it for this unforgettable layer cake instead.

I’ve kept the two most important components – sweet potato and marshmallow but instead of an overly sweet, sloppy side dish I’ve turned them into a show stopping centerpiece. If you’re new to using sweet potatoes in your baking, I got you. You could ease yourself in with a classic Sweet Potato Pie or dive right in with this sweet potato layer cake to impress your guests this fall.

At the heart of this cake is the sweet potato puree. I’ve used fresh for this recipe as not only do they give it that rich, festive color but provide the cake with a natural sweetness. Warm spices including cinnamon, all-spice, nutmeg and cardamom provide the perfect pairing to your potatoes. These combined with a few pantry staples will create your moist layers of cake. Trust me, it will be a huge hit

The fluffy marshmallow frosting will sandwich your layers together as well as create that toasted blanket of beauty on the outside. While I could’ve left it as is, I couldn’t resist a crown of candied pecans and crushed walnuts to add a rustic flair. Even the fussiest of dessert fans will be begging for your recipe.

I know it can be tough pleasing all ages and tastes around the Thanksgiving table but there is one thing they will all agree on this year - this sweet potato layer cake is unforgettable. 

WHY WE LOVE THIS SWEET POTATO LAYER CAKE

• Different & delicious – It’s guaranteed to both shock and delight your loved ones that you’ve used sweet potatoes in a cake, not to mention it’s a refreshing change from the same old pumpkin puddings and pumpkin cake!
• Customizable – Not a fan of cinnamon? Skip it. Intimidated by marshmallow frosting? Check out my mascarpone frosting instead. Prefer cupcakes to a layer cake? No problem. As always, this recipe can be customized to your tastes, skills and budget.
• Showstopping Centerpiece - Inspired by my smores layer cake, the marshmallow frosting not only adds drama but brings a sweet contrast to the cake’s warming fall flavor. Topped with a crown of candied pecans that heighten the Fall aesthetic while adding crunch to each savored mouthful. There’s no arguing this cake deserves center stage on your table this year. And the next. And the next.
• Perfect for Thanksgiving – Make ahead friendly? Check. Crowd pleasing flavors? Check. Rustic fall aesthetic? Check. Some would say this is the perfect Thanksgiving dessert or decadent dessert for the holiday season.

INGREDIENTS/SHOPPING LIST 

Sweet Potato Layer Cake 

• sweet potato puree (from 2 large sweet potatoes)
• all purpose flour or cake flour
• baking soda
• baking powder
• salt 
• cinnamon
• all-spice
• ground nutmeg
• cardamom 
• butter
• vegetable oil- canola oil can be used as well
• sugar
• vanilla
• buttermilk
• walnuts, toasted pecans, or candied pecans

Homemade Marshmallow Frosting 

• sugar 
• light corn syrup
• egg whites
• cream of tartar
• salt
• vanilla

SUBSTITUTIONS AND ADDITIONS

• Sweet potatoes – If using fresh sweet potatoes, either roasted or boiled works. By roasting them, I find the sweet potatoes will have a slightly more intense sweetness, but boiling them will keep a little more moisture. Although I find fresh will always taste better, but if you don't have time to make your own sweet potato puree, you can also use canned sweet potato puree in lieu of fresh sweet potatoes.
• Buttermilk – This recipe calls for ½ cup of buttermilk. It’s essential as the acidity of the buttermilk reacts with the baking powder and soda for an irresistible texture as well as an added tang to the flavor. To save a trip to the store, you can make homemade buttermilk by adding ½ tablespoon of white vinegar or lemon juice to ½ cup of whole milk. Wait 5 minutes for it to thicken then add it to the recipe as per directions.
• Fall Flavors – Have fun with your favorite fall flavors. I’ve used cinnamon, all-spice, ground nutmeg and cardamom but ground ginger, pumpkin spice and cloves will also work in this recipe. Alongside the warming spices, a little orange zest will work well.
• Marshmallow fluff – Do not substitute the frosting for store-bought marshmallow fluff. They might taste a little similar but they have very different textures. Marshmallow fluff is not nearly stable enough to be piped onto this cake. Plus, this homemade version is sooo good!
• Cream of tartar – Cream of tartar helps to stabilize the whipped egg whites for the frosting, but if you don’t have any to hand substitute for lemon juice. Lemon juice provides the same acidity so your frosting will still form stiff peaks. Substitute an equal amount of lemon juice for the cream of tartar.
• Frosting – Not a marshmallow frosting fan? Switch for one of your favorites instead. Try Swiss meringue buttercream, mascarpone frosting or cinnamon cream cheese frosting.

RECOMMENDED TOOLS TO MAKE THIS RECIPE 

• Baking sheet
• Aluminium foil
• Fork or potato masher
• 3 x 8-inch cake pans
• Medium sized bowl
• Large Bowl
• Spatula
• Whisk
• Cooling rack to cool cakes
• Sauce pan
• Heat proof bowl
• Serving plate

HOW TO MAKE THIS SWEET POTATO LAYER RECIPE

With its striking appearance, this sweet potato layer cake may appear overwhelming but it's surprisingly straightforward and perfect for the fall season. Make your mash, add your wet ingredients to your dry ingredients then bake and cool. Sandwich the cake layers together before swirling on more frosting ready for some torching!

Homemade Sweet Potato Puree

1. Start by preheating the oven to 425º . Add sweet potatoes to a baking sheet lined with aluminum foil, then prick all over with a fork.

2. Bake until tender (around 45 to 50 minutes) Let cool, remove the skin and smash with a fork or blend until smooth. 

For The Cake

3. Preheat oven to 350 degrees. Grease and flour three 8 inch round cake pans. 

4. In a medium sized bowl, whisk together flour, baking soda and baking powder, salt, and spices; set aside. 

5. Next, in a large bowl, beat together butter, oil, and sugar until light and fluffy. 

6. Add eggs, one at a time, beating thoroughly and scraping down the sides of the bowl before adding the next egg. PRO TIP: Ensure your eggs and butter are room temperature. This will allow your ingredients to mix easily to form a smooth batter.

7. Whisk in the sweet potato mixture and vanilla. 

8. Add half of the flour mixture to the batter and mix until combined. Add the buttermilk to the batter and mix until combined.

9. Finally, add the remaining flour mixture and mix until well combined and smooth. Scrape down the sides of the bowl as needed to ensure everything is well combined. This batter will be thick.

10. Divide the batter evenly between the prepared pans.

11. Bake cakes for 20-25 minutes, or until a toothpick inserted in the middle comes out with a few crumbs.

12. Remove cakes from the oven and allow to cool for 3-4 minutes, then remove the sweet potato cake layers from pans to a cooling rack to finish cooling.

Marshmallow Frosting

13. To make the Marshmallow Frosting, bring a small pot with 3-4 inches of water to a boil. 

14. In a large heatproof bowl (I use the metal bowl of my stand mixer), add all frosting ingredients. Place the bowl over the boiling water and whisk constantly until the sugar has dissolved and the mixture feels smooth and no longer grainy - about 3 minutes.

PRO TIP: Make sure your heatproof bowl is completely clean and the bottom of it does not touch the hot water when resting on top.

15. Remove bowl from heat and beat the mixture on high speed until it has doubled in size, is no longer warm and forms glossy, stiff peaks - about 5 minutes. 

PRO TIP: If you’re struggling to form stiff peaks, it’s possible that there was grease in your bowl or whisk, or water got in the bowl. Whip for a short while longer, if still no peaks form you may need to start the frosting over.

To assemble

16. To assemble the cake, place the first cooled cake layer on a serving plate or cardboard cake circle. Add about a cup of marshmallow frosting, then spread in an even layer using a spatula.

17. Top the frosting with the second layer of cake and repeat with another layer of frosting.

18. Add the final layer of cake, then frost top of cake and the entire outside. PRO TIP: I recommend using an offset spatula, pulling upwards as you spread to create decorative peaks and swirls.

19. If possible, refrigerate the cake for 1 hour. 

20. Right before serving, toast the outside of the cake with a kitchen torch. If desired, garnish the top rim of the cake with crushed nuts. 

21. Serve and enjoy! 

TIPS 

• Make ahead – You can make the sweet potato puree and cake layers in advance. The cake layers will freeze for up to 2 months. However, I would recommend making the frosting the same day as assembling the cake for best results.  
• Torch Tips – We want a golden brown finish not a black crispy coating so make sure to use the torch close to the cake but in quick, gentle movements to avoid burning.
• No torch? No worries - You can still serve your cake with the marshmallow frosting as is, but I can’t lie, toasting the frosting is the most fun part! If you don’t have a kitchen torch adjust your oven rack and set your oven to broil. Broil until golden around 1 to 2 minutes, then refrigerate the cake for 15 minutes.
• A little garnish goes along way – the marshmallow frosting can easily do all the talking, so you can keep the garnish to a minimum. I prefer a simple crown of candied pecans or crushed walnuts as a final finishing touch.
• Switch up the shape – Instead of a layer cake, you can use this recipe for a sheet pan cake or even cupcakes with smaller swirls of toasted marshmallow frosting. You will need to adjust your baking time (keep an eye at around 20 minutes.)

STORAGE TIPS 

• I would recommend serving this cake within a few hours of assembling it otherwise you risk the frosting structure going runny. If you have any leftovers, they can be kept at room temperature for up to 2 days.
• If you make your cake layers ahead, wrap the cooled cake separately in 2 layers of plastic wrap. Then add them to a zip-loc bag and freeze for up to 2 months.

FREQUENTLY ASKED QUESTIONS

Can you use pumpkin in this recipe instead of sweet potato?

Although I haven’t tried this layer cake with pumpkin, I don’t see why you couldn’t use it in this recipe. Both sweet potato and pumpkin offer similar texture, color, and taste when used in baking. They also both work fabulously with the fall flavors of this recipe. However, I prefer sweet potato as it brings a more rich flavor and a creamier texture. If you’re craving a pumpkin sweet treat, check out my pumpkin flan cake or my Pumpkin Dulce de Leche Cake. If you do give this recipe a try with pumpkin, let me know in the comments how it goes!

What is the difference between marshmallow topping and meringue?

While both are made using the same ingredients there is a key difference. Meringue topping like the style used on my lemon meringue pie bars involves whipping the egg whites and sugar but then layering it on top and baking until browned.

Whereas marshmallow topping on the other hand is made slightly differently. Made using a double boiler, you essentially cook the egg whites as you beat them over the boiling water. Beating at a high speed and temperature transforms the egg whites into a super fluffy and silky mixture just like a marshmallow!

Then for the fun, finishing touch. To create that irresistible, just-toasted topping you can use a kitchen torch or broiler.

How do you make candied pecans?

Candied pecans can be baked in the oven or cooked on the stovetop. I find the stovetop easiest as you can keep an eye to avoid burning. Add brown sugar, water and a little cinnamon to a skillet and stir until the brown sugar melts and begins to bubble. Stir in the pecans until coated evenly. Transfer to a baking sheet to cool then break before adding to your cake.

Who started the sweet potatoes and marshmallows combination?

There’s no question it’s a unique combination, but founder of the Boston Cooking School magazine, Janet McKenzie Hill, pioneered the sweet potato and marshmallow side dish. Hired by the marketers of Angelus Marshmallows in 1917, her role was to develop recipes for a booklet that encouraged more marshmallows in our everyday cooking.

It was in this booklet that mashed sweet potatoes with a marshmallow topping first appeared. Immediately it divided the nation, but needless to say, marshmallow sales went through the roof.

MORE THANKSGIVING RECIPES YOU MAY ENJOY

•  Sweet potato pie with marshmallow topping
• Thanksgiving turkey roulade
• Sweet potato cheesecake
• Pumpkin Streusel Cheesecake Bars