Japanese Sweet Potato Butter Mochi (Mochi Cake)
This Japanese sweet potato butter mochi is a twist on local Hawai’i style butter mochi, which is an easy, shareable mochi cake. Add a roasted Japanese sweet potato for a smooth texture and nutty flavor. Plus, it’s naturally gluten-free! Disclaimer: This post contains affiliate links.
What is Butter Mochi?
Butter mochi originates from local Hawai’i cuisine and has roots in Japanese and Filipino foods. It’s essentially a snack cake, typically baked in a rectangular baking pan and cut into squares like brownies. It’s made with a glutinous rice flour called mochiko, which is made from the same rice that you make mochi from! The texture is chewy, dense, and bouncy. Please note: if you’re looking for a stretchy, elastic mochi, you’ll want to check out my chi chi dango recipes instead.
A classic butter mochi is made with basic cake ingredients: eggs, milk, butter, etc. Its flavor is similar to a basic vanilla cake.
Because I add roasted sweet potatoes to this recipe, it has a slightly nutty flavor and golden brown color. Brown sugar instead of white sugar adds a more caramelized, molasses-y flavor as well. Ugh, I’m drooling just writing about it.
Japanese Sweet Potato vs. Purple Sweet Potato vs. Ube
Talking about Japanese sweet potatoes is the source of much confusion on the internet. The Japanese sweet potatoes I’m talking about for this recipe are murasaki variety potatoes, with a purple skin and a very light colored flesh. These are different from other purple sweet potatoes, such as the Okinawan sweet potato, which has a light brown skin and purple flesh.
Still, these are different from ube, which is not a potato at all but a purple yam!
I actually already have recipes for a purple sweet potato butter mochi and an ube butter mochi, so go check those out if that’s what you were looking for!
How to Prepare Japanese Sweet Potatoes
This recipe called for a Japanese sweet potato that has already been roasted. Typically, I will roast my sweet potatoes the day before and serve it as a side dish for dinner. Leftover potatoes keep really well in the fridge, and the next day I can scoop out the flesh to make desserts like this butter mochi. Super easy!
And you can roast Japanese sweet potatoes the same way you roast other potatoes: I usually do one hour at 425 degrees F.
Other Ingredient Notes
I often get asked if mochiko is the same as sweet rice flour, but the answer is not so simple. Glutinous rice is sometimes called sweet rice, so yes, they can be the same thing. However, you can make different types of flours with the same rice, and they will result in different end textures. For this recipe, I recommend specifically using mochiko and not other types of glutinous rice flour. I typically use the Koda Farms brand, but Shirakiku is okay as well.
Feel free to substitute other milks for the milks listed in this recipe. Butter mochi is very forgiving. My only advice, however, is to try to stick with more rich milks. Coconut milk has a lot of fat, so you wouldn’t want to substitute it with something super thin like almond milk.
How to Make Sweet Potato Butter Mochi
Butter mochi is notoriously easy to make. Typically you just mix dry ingredients, then mix wet ingredients, then add the mixtures together, and bake! To be honest, I’ve cheated before and thrown everything all into one large bowl and it’s been fine too.
For this recipe I only have one extra step if blending the roasted sweet potato to make it extra smooth. Roasted Japanese sweet potatoes are so soft, however, that you could probably skip this step if you wanted to and just mix it in by hand or mash it up with a fork. You may get a few chunks in your final mochi, but I mean, I wouldn’t really complain about that.
Lastly, I sprinkled the top with black sesame seeds. Sweet potato and sesame is a common flavor pairing in East Asian foods (like my daigaku imo recipe!). But you can totally skip this step if you want.
More Butter Mochi Recipes
They don’t call me Mochi Mommy for nothing. Check out these other butter mochi recipes:
- Matcha Butter Mochi
- Chocolate Butter Mochi
- Birthday Cake Butter Mochi
- Classic Local Hawaiian Butter Mochi
Roasted Japanese Sweet Potato Butter Mochi
Ingredients
- 8 oz mochiko, see notes
- 1 tsp baking powder, 5g
- 1/2 tsp kosher salt, 3g
- 12 oz roasted Japanese sweet potato
- 6 oz evaporated milk, half a standard size can in the US
- 1 14oz can coconut milk
- 6 oz brown sugar, roughly 3/4 cup packed
- 2 eggs
- 2 oz unsalted butter, melted, 4 tbsp
- 1 tsp vanilla extract
- 1 tbsp black sesame seeds, optional
Equipment
- Blender
- 9×9" metal baking tin can sub 8×8"
Instructions
- Preheat oven to 350 degrees F. Grease and line a metal 9×9" baking tin.
- In a mixing bowl, whisk mochiko, baking powder, and salt.
- Peel roasted sweet potato and place flesh in a blender with evaporated milk. Blend until smooth; it'll have a creamy, soft-serve like consistency.
- Place blended sweet potato in the mixing bowl along with coconut milk, brown sugar, eggs, melted butter, and vanilla extract. Mix well.
- Pour batter into your prepared baking tin. Sprinkle black sesame seeds on top if you wish.
- Bake for 45 minutes or until a toothpick poked through the center comes out clean. Allow to cool before slicing. Leftovers can be kept in an airtight container at room temperature.
Notes
- 8 oz of mochiko is half a one pound box by weight. Please use a digital scale to measure. If you don’t have a scale, it’s close to 1 and 3/4 cup.
- Some readers have mentioned that glass, disposable, and ceramic baking dishes do not bake the mochi through the center before the edges burn. I recommend using a metal baking tin.
- 12 oz of sweet potato was one medium sized potato for me.
- This recipe did not include roasting time, as I used a leftover roasted sweet potato that I had kept in the fridge. If you still need to roast your sweet potato, you’ll need to add an hour of cook time. Wash your sweet potato very well, poke holes in it, and bake at 350 degrees F for one hour. I recommend roasting a large batch for snack or to eat with a meal and use the leftovers to make my sweet potato dessert recipes.
- You can double this recipe to fit in a 9×13″ baking dish.
I just made this recipe for a friend who had a gluten/nightshade allergy. I doubled the recipe, and used once can of coconut milk and 1 can filled with whole milk because I didn’t have a second can of coconut! I baked it in a disposable aluminum pan, and it took about twice the amount of time to bake through, but it worked well!