Sweet Potato Cake with Walnuts & Marshmallow

Cut the sweet potatoes first—roasted or boiled, doesn’t matter much. Three hours before you even think about the mixer. This cake needs them cold. Or room temp. Honestly either works, but cold makes spreading frosting less of a mess.

Why You’ll Love This Sweet Potato Cake

Takes an hour and a half total. Most of that’s oven time, so you’re not standing around. The cinnamon hits before anything else—just enough to make you wonder what that smell is, then you remember. Marshmallow frosting. Not buttercream. Not cream cheese. Actual marshmallow, which means it stays fluffy even after a day in the fridge. Walnuts in the batter and on top, which sounds redundant but isn’t. One set softens into the crumb. The other stays crunchy. Works cold. Works room temperature. Tastes different both ways—richer when it’s warm, lighter when it sits overnight.

What You Need for This Sweet Potato Dessert

Flour—two cups, all-purpose. Nothing fancy. Baking soda. One teaspoon. Not baking powder. The difference matters here. Cinnamon. Ground. One and a half teaspoons. More if you want the spice louder. Sugar. Granulated. A cup and a quarter. Almond oil instead of vegetable. Adds something subtle. Vegetable oil works if you don’t have it, but almond’s better. Three eggs. Large. Room temperature helps them mix smoother. Two cups mashed sweet potatoes. Cooked. Cold is fine. The starch is what matters. Walnuts. Chopped. One cup, but save some for the top—half a cup maybe, unground.

For the marshmallow frosting: unsalted butter (half cup, soft), marshmallow cream (seven ounces), powdered sugar (three cups), salt (just a pinch).

How to Make Sweet Potato Cake

Heat your oven to 350. Spray a 9x13 pan. Light coat. Not dripping.

Mix the dry stuff—flour, baking soda, cinnamon—in a big bowl. Sift it. Whisk it after. Lumps will ruin the texture. Takes two minutes. Worth it.

Grab the mixer. Beat sugar and almond oil together until it looks glossy. Two minutes on medium speed. It should look bonded, slick. This is the base for everything that comes next.

Crack eggs in one at a time. Beat after each one. Watch the batter—it’ll firm up as the eggs incorporate. Stop when it looks smooth. Don’t go crazy on the mixer or you’ll work air out that you actually want.

Dump all the flour mixture in at once. Low speed. Mix until barely combined. Overmix and the cake gets tough. It’s a real problem. You’ll regret it.

Scrape the sides with a spatula twice. Get the flour that’s sticking to the edges. Then fold in the mashed sweet potatoes by hand and the chopped walnuts. Folding keeps everything aerated. Folding is slower, better for this.

How to Get Sweet Potato Cake Perfectly Baked

Pour everything into the pan. Smooth it out. Smack it gently once or twice to settle the air bubbles. Not hard. Just to level it.

Slide it in the oven. 55 minutes. Give or take a few. Every oven runs hot or cold.

Look for the edges pulling away slightly from the pan sides. The top should be golden brown with a slight crackle. Insert a toothpick near the center—clean is perfect, a few moist crumbs are fine too. If it’s wet, give it another five minutes.

Pull it out. Let it cool completely in the pan. This is non-negotiable. Warm cake plus frosting equals a disaster. Patience. Just wait.

Once it’s cold, frosting time.

Sweet Potato Cake Frosting and Tips

Beat butter until pale and fluffy. Soft but not melting. Temperature is critical here—if it’s too warm, the frosting breaks. If it’s too cold, it stays grainy.

Add the marshmallow cream. Mix steady and smooth. Don’t overmix or it goes slimy and weird. You’ll know when to stop.

Add powdered sugar in thirds. Mix each batch before dumping the next. Last step: sprinkle salt. Cuts the sweetness so it’s not cloying.

Spread it on the cooled cake. Edges can be rustic. Doesn’t matter. The marshmallow smell hits right away and that’s when you know it’s working.

Top with the reserved walnuts. Crunch and presentation. Refrigerate for at least 30 minutes so the frosting sets up before slicing.

Bring it to room temperature before serving. The cake firms when cold, flavor deepens too. Different cake than it was an hour after cooling.

Sweet Potato Cake with Walnuts & Marshmallow

By Emma

Prep:

35 min

Cook:

55 min

Total:

1h 30min

Servings:

12 servings

Ingredients

• 2 cups all-purpose flour
• 1 teaspoon baking soda
• 1 1/2 teaspoons ground cinnamon
• 1 1/4 cups granulated sugar
• 3/4 cup almond oil (substitute for vegetable oil)
• 3 large eggs
• 2 cups cooked mashed sweet potatoes
• 1 cup chopped walnuts (instead of pecans), reserve some for topping
• For frosting===
• 1/2 cup unsalted butter, room temperature
• 7 ounces marshmallow cream
• 3 cups powdered sugar
• Pinch of salt

Method

1. 1 Preheat oven to 350 degrees Fahrenheit. Spray a 9x13 baking dish lightly with nonstick spray. Airy grease coat but don’t overdo.
2. 2 In a large bowl, sift together flour, baking soda, and cinnamon. Whisk until uniform. Keeps lumps out, critical for texture.
3. 3 Grab a mixer and beat sugar with almond oil until glossy and bonded, about 2 minutes medium speed. Almond oil adds subtle nutty layer.
4. 4 Add eggs one at a time, beating after each. Watch for batter firming, don't overmix—add air but no breakage.
5. 5 Dump entire flour mix into wet ingredients at once. Hold mixer low speed, mix until barely combined. Overmix will toughen cake.
6. 6 Scrape sides down with a spatula twice to gather any missed pockets of flour. Then fold in mashed sweet potatoes and chopped walnuts carefully. Folding keeps batter aerated.
7. 7 Pour batter evenly into pan. Smack gently once or twice to level, settle air bubbles.
8. 8 Slide into oven. Bake 55 minutes give or take. Look for edges pulling away slightly from pan, golden brown top with slight crackle. Insert toothpick near center; clean or a few moist crumbs okay.
9. 9 Let cake cool fully in pan. Warm cake frosting disaster. Patience here seals the deal.
10. Frosting
11. 10 Beat butter until pale and fluffy with electric mixer. Soft but not melting butter; temperature critical for good creaming.
12. 11 Add marshmallow cream. Mix steady until slick and smooth. Resist temptation to overbeat, marshmallow will go slimy.
13. 12 Gradually add powdered sugar in thirds, mixing each addition fully before next dump. Sprinkle salt to cut sweetness.
14. 13 Spread buttercream onto cooled cake generously. Edges can be rustic; the marshmallow aroma should hit right away.
15. 14 Sprinkle reserved walnuts on top for crunch and presentation. Refrigerate cake to set frosting at least 30 minutes before slicing.
16. 15 Bring to room temp before serving for best bite texture. Watch out: cake firms and flavor deepens with resting.

Nutritional information

Calories

830

Protein

8g

Carbs

110g

Fat

42g

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Frequently Asked Questions About Sweet Potato Cake Recipe

Can I use canned sweet potato puree instead of making my own? Yeah. One-to-one swap. Canned’s thicker sometimes, so check consistency. If it looks too wet, drain it a bit. Works fine either way.

What if I don’t have almond oil? Vegetable or canola. The cake just won’t have that walnut-y undertone. Not a big deal. Still tastes good.

How long does this keep? Four days in the fridge, covered. Five if you’re lucky. After that it dries out. Freezes fine for a month though.

Can I make this without walnuts? Pecans work. Almonds work. Or just skip them and add nothing. Cake’s still good. Just less texture.

Why marshmallow frosting and not regular buttercream? Marshmallow stays fluffy. Buttercream gets dense when it sits. This frosting actually improves overnight—fluffier, lighter. Try it once and you’ll see.

Does this work as a sheet cake for a crowd? Yeah. Feeds maybe twelve people if you’re cutting normal-sized pieces. Nine if everyone’s hungry. The frosting covers the whole thing so presentation’s easy.

Can I add chocolate to this? Half a cup of cocoa powder mixed into the dry ingredients. Or chocolate chips folded in with the walnuts. Turns it into something between a sweet potato cake and chocolate brownie. Both versions work.

How do I know when it’s actually done baking? Edges pull away from the pan. Top’s golden with a slight crack. Toothpick in the center comes out clean or with a few crumbs stuck. Don’t wait for the toothpick to be completely dry or you’ll overbake it.