Sweet Potato Cake With Toasted Marshmallow Frosting

November 11, 2020
4 Ratings
  • Prep time 4 hours
  • Cook time 40 minutes
  • Makes one 13x9-inch cake
Author Notes

Sweet potato sheet cake is the easy-peasy dessert you didn’t know you were missing. Not unlike its vegetable-forward cousins, carrot cake and pumpkin cake, sweet potato cake is incredibly moist, due to—you guessed it—mashed sweet potatoes. This ingredient has the most gorgeous of orange hues, with an earthy, vegetal flavor. If you top it with loopy swirls of marshmallow frosting, not only will your finished cake be beyond beautiful, but those on-the-fence about a cake that doesn’t include the word "chocolate" (um, me) will be begging for seconds. Promise.

The cake is oil-based (another factor contributing to its moistness) and comes together in two bowls. I call for more brown sugar than white, as molasses-y flavors go so well with sweet potatoes, plus all the fall spices (cinnamon! nutmeg! ginger! allspice!), and an extra egg yolk for richness.

On the off chance you’re not feeling a cake that requires cooking sweet potatoes in advance, I got you. First, you can just buy canned sweet potatoes. You should be able to find them easily in the organic section of the grocery store, if not in the conventional canned goods aisle.

Or, you could prepare them my favorite way: in the microwave. I poke one sweet potato all over with a fork, then microwave it on a small microwave-safe plate. Cook on high for 8 to 10 minutes, flipping the potato at the halfway point, until squishy when you give it a little squeeze. This way is the fastest, but if you’d rather use your oven, check this out this how-to guide.

Finally, while I adore everything and anything with the word "marshmallow" in it, if a sweet potato cake crowned with tangy cream cheese frosting is more your speed, by all means go for it. This one would be quite lovely, just sayin’. —Jessie Sheehan

What You'll Need
  • Sweet Potato Cake
  • 2 3/4 cups all-purpose flour
  • 1 3/4 teaspoons baking powder
  • 1 teaspoon kosher salt
  • 1/4 teaspoon baking soda
  • 2 teaspoons ground cinnamon
  • 3/4 teaspoon ground nutmeg
  • 1/2 teaspoon ground ginger
  • 1/4 teaspoon ground allspice
  • 1 cup vegetable oil
  • 1 1/2 cups light brown sugar
  • 1 cup granulated sugar
  • 2 teaspoons pure vanilla extract
  • 3 large eggs
  • 1 large egg yolk
  • 2 cups sweet potato purée (from about 1 pound whole potatoes, or canned)
  • Marshmallow Frosting
  • 3 large egg whites
  • 1 1/2 cups granulated sugar
  • 1 1/2 teaspoons light corn syrup
  • 1/2 teaspoon cream of tartar
  • 1/4 teaspoon kosher salt
  • 1/4 cup water
  • 1 teaspoon pure vanilla extract
  1. To make the cake, heat the oven to 350°F. Grease a 13x9x2-inch pan with non-stick spray or soft butter. Line the bottom with parchment paper.
  2. In a medium-sized bowl, whisk together the flour, baking powder, salt, baking soda, and spices.
  3. In a large bowl, whisk together the oil, sugars, and vanilla. Add the eggs and yolk, one at a time, and continue whisking until smooth. Add the sweet potato and whisk again.
  4. Add the dry ingredients to the wet in three installments and, using a rubber spatula, gently fold to combine just until the flour disappears—do not over-mix.
  5. Transfer the batter to the prepared pan and smooth the top with an offset spatula or butter knife. Bake for 30 to 35 minutes, rotating at the halfway point, until a cake tester comes out with a moist crumb or two.
  6. Let cool until easy to handle, then run a butter knife around the edges, releasing it from the pan. Invert the cake onto a cooling rack, flipping it right side up to cool to room temperature.
  7. At this point, the cake will keep at room temperature, tightly wrapped, for up to 2 days. Hold on the frosting until you’re ready to eat.
  8. To make the frosting, add the egg whites, sugar, corn syrup, cream of tartar, salt, and water to the bowl of a stand mixer and place the bowl over a saucepan of simmering water over medium heat. Do not allow the bottom of the bowl to touch the water.
  9. Whisk constantly until the sugar melts and the mixture is warm to the touch, 3 to 5 minutes. Remove the bowl from the heat and place the bowl on the stand mixer fitted with the whisk attachment. Beat the egg white mixture on high speed until stiff and glossy, 5 to 7 minutes. Add the vanilla and continue beating until just combined.
  10. Use a spoon or offset spatula to generously frost the cake. Toast the frosting using a kitchen torch or by placing the frosted cake under the broiler briefly, until browned.
  11. The frosted cake is best served within a few hours, as the frosting loses structure over time, but any leftovers will keep on the counter lightly covered for up to 1 day.

See what other Food52ers are saying.

  • FrugalCat
  • Jessie Sheehan
    Jessie Sheehan
  • katemassot
  • adrienne
Bio: Jessie Sheehan is the author of The Vintage Baker and Icebox Cakes. Her new easy-peasy baking book, Snackable Bakes, hits shelves in spring 2022. She contributes to the Washington Post, Bon Appétit, Food Network, and the Kitchn, among others.

10 Reviews

katemassot July 5, 2023
This is the best cake I’ve ever had! Easy to follow recipe and it comes together perfectly every time. I’ve had so many people ask for this recipe because it really is INCREDIBLE. (i bet it would be great with cream cheese frosting too!)
Jessie S. July 5, 2023
So happy you like this cake so much! And agree: cream cheese frosting would be great.
adrienne January 16, 2022
This cake was so moist and delicious. Take your time with the frosting though or it will be gritty! Cool it completely and let the top dry slightly before frosting or it will get gooey underneath. Second time around and it was HEAVEN!
Jessie S. July 5, 2023
Yay! And thanks for your tips!!
FrugalCat November 16, 2020
Halved the recipe (2 eggs, no extra yolk) and baked it in cupcake pans. For a couple of them I just put a marshmallow on top during the last 10 min of baking. That came out pretty well. Fir the others, I frosted them with marshmallow fluff from the jar, then bruleed them with a mini torch. Both frostings were fine (I'm not a big icing person) but honestly, this didn't need anything on top.
Sarah M. November 16, 2020
I like the cupcake idea for portability!
Jessie S. November 16, 2020
yay! so glad you made the cake into cupcakes and so glad you felt the cake didn't even need frosting! XO
Jessie S. November 16, 2020
Yes! Me too.
J January 17, 2021
and to riff off the above, not everyone owns a stand mixer. it would be nice if F52 recognized that
Jessie S. January 17, 2021
Great point! Thank you.