Goguma cake is something you often see at Korean cafes but I've never seen a recipe for it. (Of course, I've only been searching English language sites—there must be some very good ones on the Korean language ones.) Undeterred, I decided to MacGyver up a recipe. I mean, how hard could it be? After all, gogumas, or Korean sweet potatoes, aren't too far off from bananas, so wouldn't a banana cake recipe work just as well? After some research, I had a hunch that the most workable banana cake recipe would be Martha Adams's version in Cooking From Quilt Country. It uses cake flour and turns out a very light, wonderful cake.
Of course, I ended up having to substitute more than just the bananas—I didn't have buttermilk. But lack of buttermilk is never a deal-breaker. I've always found that a combo of yogurt and half-and-half does a pretty good job as a buttermilk sub, and those two things were luckily in the fridge. Now the only difficulty in making this cake is that you have to have precooked gogumas. I had some leftover from a couple of days before, and really, it was trying to figure out what to do with it that led me to making this cake.
In case you've never eaten a Korean (or Japanese) sweet potato, let me warn you that it is very different from American red sweet potatoes (sometimes called yams). A goguma's flesh is light golden and its sweetness is more delicate, less in-your-face. And there's a natural buttery richness so that if you simply roast one, you can eat it plain. Fantastic as part of a tempura platter too.
Another warning: this cake recipe is a bit more involved than a banana cake recipe because you need to put the cooked goguma through a sieve (chinoise) otherwise you just end up with too much fiber in the cake.
So, here we go!
Adapted from Cooking From Quilt Country by Marcia Adams
Goguma Cake
2/3 cup of butter
1 cup sugar
3 eggs at room temperature
2 1/4 cups of sifted cake flour
1 1/4 teaspoons of baking powder
1 1/4 teaspoons of baking soda
1 1/4 teaspoons of salt
2/3 cup of buttermilk at room temperature (or a combination of plain yogurt and milk or half-and-half)
1 1/4 cups goguma, cooked, mashed, and sieved
2/3 cup of chopped walnuts
Preheat your oven to 350 degrees. Cream the butter and sugar until fluffy. Add the eggs one at a time, beating well. Sift the dry ingredients together. Add a third to the butter mixture and beat. Then add a third of the buttermilk (or sub) and beat. Then a third of the dry, then a third of the wet, etc. Add walnuts, mix, put in a pan (I used a brownie pan but you can use two cake pans) and bake.
In a brownie pan, the cake should take about thirty minutes, depending on your oven. You want to keep the cake pretty light and tender, so check after twenty. I always use a cake tester. Of course, you are perfectly free to frost the cake if you wish (any type of frosting will do), but I like mine with just a dusting of powdered sugar.
