Japanese Sweet Potato Cakes

Muffin-shaped Japanese sweet potato cake. Yummy!

The Japanese sweet potato (サツマイモ), which I've extolled the tasty virtues of before, is relatively cheap and easy to purchase year-round though it is cheaper in the fall. The main problem with them is that they are hard to cook and handle in a fashion which leaves you with a tasty result. This is likely more so the case if you're a foreigner and don't know how to prepare them though, if my students are any indication, most Japanese women don't know much about cooking these days either.

For this reason, I tend to get my sweet potatoes pre-prepared from more skillful hands but I can't help but recognize how much cheaper it'd be for me to make dishes with them myself. To that end, I decided to try and make Japanese sweet potato cakes. I've bought these from markets and had them as souvenir gifts from co-workers before and enjoyed them. However, there's a real quality difference based on the source of such pre-made "sweets" and I'm guessing I never had a top of the line cake.

The main problem with cooking Japanese sweet potatoes is that they are extremely dry inside. I've read that the peel is also quite bitter. If you bake them or microwave them, they become almost unpalatably dry. If you boil them, they tend to disintegrate too easily. I did some research on the internet and found a recipe from a Japanese woman (Setsuko Yoshizuka) on about.com which contained what I believe is an authentic recipe. I decided that I'd follow it to the letter as best I could and hope for the good results.

Japanese sweet potato steamed and peeled.

The first thing that she says you should do is steam two small potatoes before peeling them. This is something I've seen on Japanese cooking shows before but western people usually don't handle potatoes in this fashion. In the west, we tend to peel and boil, or, at best, peel and steam, but I've heard that it's better to steam all types of potatoes because they won't absorb water and diminish the flavor of the resulting product. I found that the skin easily peels off when you steam the whole tuber so you don't waste the flesh as you do when you peel a raw potato. The only down side is that it takes a long time to steam a whole potato to a tender state.

Peeled and sliced potatoes ready for mashing.

The peeled potatoes look a bit dirty and nasty because the purple flesh stains the outside and they're rather hard to mash because they are so dry.


At first, I tried to mash them just with a fork but it resulted in a lot of what appeared to be little pebbly globs so I added the butter in the original recipe to moisten it up a bit then started bashing it with a large whisk. While this was better, adding milk helped a bit. In the end, I decided to triple the milk from 1 tbsp. to 3 tbsp. because it was not very smooth. I think that this was because my sweet potatoes were not as small as they might have been (though, honestly, based on my experience buying these potatoes, they were quite small). In the end, it was still very stiff for mashed potatoes.


The original recipe called for the cakes to be formed and placed in aluminum oval-shaped tins. You can get these disposable tins in most markets but I didn't have any on hand and I figured they're mainly for aesthetic purposes and for super easy removal. I buttered up 4 muffin tins and pressed the potato into them though not too firmly as I didn't want the cakes to be too dense. I ran a fork over the top for some sort of vague pattern and brushed it with egg and water as instructed. One tip I can offer is that you don't need to reserve any egg yolk for brushing as the recipe says. If you put the yolk in a small bowl and beat it a bit then pour it into the potatoes, there will be enough of a residue in the dish to mix with about 4 or so drops of water to use as a "glaze". In the picture above, the potato cake puffed up a bit above the lip of the muffin tin but the finished cakes sink back down after they have cooled. My main concern was about whether or not they'd un-mold cleanly from the tins but they were fine. However, I did butter them liberally so that was to be expected.

The original recipe recommended baking the cakes for 10-15 minutes at 190 degrees C. (375 degrees F.) but I felt that that wouldn't be long enough given the shape of my cakes. I believe the shorter time would work fine with the longer, shallower oval-shaped cakes but wouldn't allow heat to penetrate to the center of my muffin-shaped ones so I gave them 25 minutes. I mainly decided to monitor how brown the top got and to pull them out if they started to look dark.

The interior of the cake.

The top of the cake looked exactly like it was supposed to and the texture (moist but just a bit light) was precisely the same as the pre-prepared cakes I have had before. The only difference was that it was much, much better because it was fresh and did not have added chemicals in it for long-term preservation. No one could be more surprised than I that this was a complete success the first time out. I guess it was a tribute to the simplicity of the original recipe. It perhaps was hard to mess up.

The main problem with these cakes is that making them way I did by hand the entire way was very labor-intensive. I'm going to make them again but next time I'll use my mixer for the mashing. The main recipe is also very basic (2 potatoes, 2 tbsp. butter, 1 tbsp. milk, 2.5 tbsp. sugar, 1 egg yolk) and I think that adding just a little brandy (1-2 tsp.) might sharpen up the sweet potato flavor and add a certain richness to them. The only modification I made this first time out was that I used brown sugar instead of white sugar since I believe it pairs better with sweet potato.

Those who think of a sweet which is called a "cake" as being like, well, cake, may be disappointed in this. The texture is more like the filling of a sweet potato pie. That's not to say it isn't very nice. Like many Japanese sweets, the sweetness is light and there's more nutrition to them than the average western sweet. They make for a wonderful, filling treat with tea. If you have friends over who aren't fans of heavy sweets or who are watching calories and want to surprise them with a treat, this would be a super dessert. They also make a fiber-rich, carbohydrate-dense breakfast treat.