Prepare the sweet potato: Peel the sweet potato and cut it into small cubes. Steam in a bamboo steamer (or any steamer) until soft.
Make the batter: In a bowl, combine the soy milk, vegetable oil, and a pinch of salt. Sift the flour, baking powder, and sugar into the bowl. Mix gently until smooth. Add the steamed sweet potato and fold until evenly combined.
Steam the cakes: Place cupcake liners in your steamer. Spoon about two tablespoons of batter into each liner.Cover and steam on medium heat for about 15 minutes, or until a toothpick comes out clean.
Serve: Remove the cake from the steamer and let it cool. Enjoy!
Notes
This recipe uses a bamboo steamer, but any type of steamer will work.
The batter is steamed directly in cupcake liners, though cupcake molds will give you a cleaner, more defined shape.
For a tasty variation, try making this recipe with kabocha squash instead of sweet potato.