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Prep time
4 hours
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Cook time
40 minutes
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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
Ingredients
- Sweet Potato Cake
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2 3/4 cups
all-purpose flour
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1 3/4 teaspoons
baking powder
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1 teaspoon
kosher salt
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1/4 teaspoon
baking soda
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2 teaspoons
ground cinnamon
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3/4 teaspoon
ground nutmeg
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1/2 teaspoon
ground ginger
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1/4 teaspoon
ground allspice
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1 cup
vegetable oil
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1 1/2 cups
light brown sugar
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1 cup
granulated sugar
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2 teaspoons
pure vanilla extract
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3
large eggs
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1
large egg yolk
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2 cups
sweet potato purée (from about 1 pound whole potatoes, or canned)
- Marshmallow Frosting
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3
large egg whites
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1 1/2 cups
granulated sugar
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1 1/2 teaspoons
light corn syrup
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1/2 teaspoon
cream of tartar
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1/4 teaspoon
kosher salt
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1/4 cup
water
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1 teaspoon
pure vanilla extract
Directions
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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.
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In a medium-sized bowl, whisk together the flour, baking powder, salt, baking soda, and spices.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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.
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