What can I say about this delicious purple sweet potato cake? This was one of my most adventurous holiday recipes, but it produced the most rewarding dessert I ever had on my table! I just had to share it with you! This cake had been on my todo list for a while but I held off and had to do a lot of extensive research to ensure this purple sweet potato cake came out perfect with the right fluffy consistency and beautiful color, not to mention the addictive taste! This sweet potato cake with the marshmallow cream cheese frosting was honestly one of my best cake recipes to date (I know I seem to say that a lot but it’s honestly how I feel!). In fact the potato cake was so good i was unable to keep some leftovers for the next day! The making of this cake can get quite technical but no need to panic, yours truly is here to walk you through the process of getting this right all the time! I will first explain the key ingredients to a successful purple sweet potato cake before moving on to the recipe. This is not one of those recipes that you want to simply skip to the recipe. If you want to make this, please take a moment to read through the tips and reasons for selecting the right ingredients. You won’t regret it!!
There are two common types of purple sweet potatoes that can be found in most Asian supermarkets or traditional grocers. One of them is the Stokes purple sweet potato, pictured here on the left. It is characterized by its distinctively purple flesh and purple skin. It is the best textured sweet potato for this recipe as it is a little dry, and somewhat fibrous (similar to a russet potato) once it is cooked. It also keeps most of its vibrant color when cook and once baked into the cake.
The other common purple sweet potato that you might think to use for this recipe is the Okinawan purple sweet potato pictured here on the right. Do not use the okinawan purple sweet potato in this recipe! As you can see there is quite a texture difference in these two sweet potatoes. The Okinawan sweet potato is creamy once cooked, and has a sweeter taste than the Stokes sweet potatoes. It also turns grey-blue once it is cooked, and when used in baking it can turn your baked goods blue.
A good substitute for the Stokes purple sweet potato in this recipe is any sweet potato with a dry/starchy consistency similar to a russet potato when cooked such as the Hannah sweet potato (a sweet potato similar in texture to the Stokes with pale skin and yellowish flesh when cooked), the Japanese/kotobuki sweet potato, and the Jewel sweet potato (not to be confused with the garnet sweet potato that has a similar orange color when cooked, but is creamy in consistency).
The summary of this little story is that when seeking to substitute a sweet potato for this recipe, go with one that has a similar texture to the one used for this cake, and not just a similar color. The reason you need a sweet potato with a drier consistency is that the cake has quite a bit of moisture from its other ingredients, and using a creamy sweet potato will result in a gummy and dense textured cake… trust me, it has happened to me before.
This cake turned out beautifully and tasted absolutely amazing with the marshmallow cream cheese frosting and the crushed walnuts and toasted mashed potato pieces.
Purple Sweet Potato Cake Recipe with Marshmallow Cream Cheese Frosting
Purple Sweet Potato Cake Sponge
- 2 ¾ cups all purpose flour
- 1 ½ cups sugar
- 2 tsp baking powder
- 1 tsp baking soda
- 1 cup cooked mashed purple sweet potato (please read text for specification)
- 1 cup milk
- ¾ cup sour cream
- 1⁄3 cup canola oil
- 2 tsp vanilla extract
- ½ tsp salt
- few drops purple food coloring (optional)
Marshmallow Cream Cheese Frosting
- 8 ounces cream cheese
- 8 ounces butter (2 sticks)
- 7 ounces marshmallow fluff
- Grease and flour two 8 inch cake pans and set aside.
- Preheat your oven to 350°F or 180°C
- Combine the flour, baking powder and baking soda and salt with a whisk and set aside.
- Using a stick blender or in a blender, blend the mashed potatoes, milk sour cream canola oil, sugar, and vanilla extract until it is smooth and properly incorporated. Don't try to do this step with just a whisk, it will not mix evenly, and it is important that it does. If you want a more vibrant cake, add a few drops of purple food coloring, otherwise, skip it.
- Combine the wet and the dry ingredients with a whisk until there are no lumps in the batter, and the cake is evenly mixed. Do not over mix!
- Split the cake mixture into the two prepared 8 inch cake pans, and bake in the preheated oven for 35-40 minutes or until a skewer inserted in the middle of the pan comes out clean.
- Allow to cool completely before frosting
To make the frosting
- Mix the cream cheese, butter, and marshmallow fluff in a mixer or with a hand mixer until it is well combined.
- Store in the refrigerator until ready to use.
- Simply assemble the cake as neatly or as rustic as you wish and decorate with leftover mashed potato pieces and toasted crushed walnuts.
I am so proud of how this purple sweet potato cake turned out and I know you will love it so….let me know how it goes when you make it! Also I’d like to know if you’ve tried other frostings outside of the marshmallow cream cheese frosting I used (which went so well with this cake, it is currently at the top of my favorite frostings list at the moment…right next to caramel). Feel free to also take a look at some of my other decadent cake recipes like my coconut caramel cake or my amazing black forest cake recipe. I hope you enjoy making this cake as much as I did!
AyobamiDecember 5, 2017 at 10:05 am
This looks stunning!!!
LoisDecember 5, 2017 at 11:07 am
Thank you so much Ayobami!!
JoyDecember 5, 2017 at 12:14 pm
I’m in awe. You go Lois! 🙂
LoisDecember 6, 2017 at 9:50 am
Thanks Joy! That is quite high praise!
Lydia from Lydia's Flexitarian KitchenDecember 6, 2017 at 6:57 am
What gorgeous photos…and that marshmallow frosting! What a great idea to use that instead of a buttercream. I have to admit I was skeptical about the texture of the cake because where I’m from sweet potato biscuits are very dense instead of light and fluffy. Your demonstration of the difference between the two varieties explains why. The sweet potatoes common to my area are very creamy when cooked so naturally they will make a heavier product…now I’m wondering what purple sweet potato biscuits would be like.
LoisDecember 6, 2017 at 11:04 am
Right Lydia! I had sweet potato cake one time and the texture was divine, I tried recreating it and it came out really gummy and dense, but I kept trying and landed on this. I can only imagine what purple potato biscuits will taste look and taste like… yum!
SarahDecember 6, 2017 at 5:19 pm
Okay- I really want to try this!!! I’m obsessed with sweet potatoes, and I think this sounds AMAZING! Gorgeous photos.
LoisDecember 7, 2017 at 8:56 am
Thank you Sarah!
Dominique | Perchance to CookDecember 6, 2017 at 5:53 pm
Oh yuuuummm, what a show stopper! This cake is calling my name! It’s beautiful and sounds so incredibly flavorful.
LoisDecember 7, 2017 at 8:57 am
ChristineDecember 7, 2017 at 10:36 pm
Oh my goodness, this is gorgeous! That icing looks delicious. Love purple sweet potatoes!
TinaDecember 8, 2017 at 10:33 am
I never would have thought to use sweet potatoes in a cake, what a GREAT idea! How fun, saving this for later.
HeleneDecember 8, 2017 at 11:41 am
We do get those sweet potato variety here!! =D
you got me drooling and in awe with your cake. The color is so attractive and I bet if you have guests over that they would not believe that this decadent and delicious looking cake includes sweet potatoes as a main ingredient.
LoisDecember 10, 2017 at 9:33 pm
You are right, the few people that got to try it (or should I say devour it), did not believe it was made with sweet potato
Emily LearyDecember 9, 2017 at 2:01 pm
WOW. Just look at the hue on that sponge. I think I’m in love. The flavours sound incredible too. I’m practically drooling on my screen here.
Abby @ WinsteadWanderingDecember 9, 2017 at 7:26 pm
The purple of this cake is gorgeous! My purple-obsessed five-year-old would love it. I’d just be over in the corner hoarding the frosting.
LynetteDecember 10, 2017 at 2:35 pm
So pretty! I would never had guessed it had sweet potato in it if you hadn’t shared all the details.
Jessica PinneyDecember 10, 2017 at 4:59 pm
Whoa, I’m lovin’ the color the purple sweet potato gives the cake. So pretty!
JulieDecember 11, 2017 at 11:10 am
This is beautiful!! Also really appreciated your sweet potato rundown – I had no idea there were two different types of purple sweet potatoes. I wonder which one we get from our CSA – I don’t remember the texture enough, but it did stay pretty vibrantly purple when we roasted it.
LoisDecember 14, 2017 at 11:03 am
Keep an eye out for the texture when next you get it. I’m sure you’ll notice the difference!
DonnaDecember 11, 2017 at 11:35 am
This is just beautiful!! I love all those gorgeous colors and that icing sounds just perfect
Mary BostowDecember 11, 2017 at 5:07 pm
What an absolute show stopper this cake is, absolutely gorgeous!
uthmanDecember 20, 2017 at 4:16 pm
The cake really look perfect Lois… You must have spent months researching on this before you finally attempted it.
LoisDecember 21, 2017 at 2:00 pm
Thanks Uthman, it took me quite a bit of time you are right, I am very happy that it worked out.
Sandra BriggsJune 20, 2020 at 3:57 pm
When do you add the sugar? My daughter (born with DS) HAS to make this for Fathers Day.
LoisJune 21, 2020 at 10:44 am
Hi Sandra! Thanks for pointing that out, I have adjusted the recipe instructions to include where to add the sugar. It is added into the wet ingredients. Let me know how it works out!
Sara StokesNovember 23, 2020 at 4:08 pm
This cake is incredible! I cannot believe how spongy and delicious it is. I used half a cup less sugar, and subbed yogurt for the sour cream because it’s what I had. I also added about a teaspoon of cardomom. I tried it with a purple sweet potato frosting recipe for a doubly purple cake. 💜
ADDecember 31, 2020 at 10:01 am
I made this cake for my coworkers yesterday and it’s great. It’s super juicy and I believe it’d be a great base for fruit cakes (e.g. apples). I skipped the frosting, because I dislike frosting in general.
However, my cake turned out green (I did not use additional food coloring). Do you have any idea why that is? The only ingredient I substituted was the canola oil. I used thistle oil instead. Did I perhaps mix the dough for too long? It took a bit until all the lumps were gone for me. I know it is a chemical reaction that can happen with purple sweet potatoes, I’m just confuses as to why it happened when I was following the given amounts precisely.
LoisJanuary 12, 2021 at 1:12 pm
You are right about it being a chemical reaction but I don’t know why it would turn green. I have never used thistle oil so that’s the only outlier I can think of that might affect the color. Even when I omitted food coloring my cake was greyish with a tinge of purple but never green. I’m glad the recipe and taste turned out great for you and your coworkers though!