Passing sweet potatoes through a sieve to puree it is too much bother, so I made a cake. Rather than a sweet potato taste, I think this cake has a simple potato taste, and is rather like a light and fluffy sponge cake version of imo-yokan (potato jelly). My mother gave this rave reviews!
Wash and peel the sweet potatoes and cut into round slices (the potatoes should weigh about 200 g at this point). Soak the potatoes in water for 5 minutes.
Whilst the potatoes are soaking, line the cake tin with kitchen parchment paper and preheat the oven to 170℃.
Add the soy mlk and drained potatoes into a pan and simmer over low heat. Once the potatoes start to soften and fall apart, mash the potatoes with a fork or spoon, and keep simmering until the potatoes have a paste-like texture.
※After simmering the water will continue to evaporate as it cools as well, so it's best to stop the heat when you think the texture is a bit softer than a custard.
Combine the eggs and sugar in a separate bowl and whisk for 1 - 2 minutes, until the mixture turns pale.
Add the vegetable oil and whisk for a further 1 minute. When it is all blended in well add the sweet potato paste and mix well with the whisk.
Add the pancake mix and keep stirring.
Pour the batter into cake tins and bake for 30 minutes at 170℃. The batter in the photos has been split between 2 mini pound cake tins and topped with black sesame seeds.
They look a bit like daigaku imo ("university potatoes", a traditional sweet potato snack.).
Story Behind this Recipe
I had 1/2 of a sweet potato leftover so I decided to make a cake with it. It weight just 250g...and I used 1 pack (200ml) of soy milk, so there are no leftovers after making this cake.
If you don't have any pancake mix, you can use 2 tablespoons of cake flour and 1/3 teaspoon of baking powder sifted together iinstead. If you only mash the sweet potato roughly, the cake will have a chunky texture.