Steam the sweet potato until tender. Leave the skin on for color and nutrients, then chop it into small bite-sized cubes.
In a mixing bowl, combine the egg, soy milk, and sweetener. Whisk until smooth.
Sift in the rice flour, baking powder, and matcha powder. Mix well until no lumps remain.
Add the diced sweet potato and raisins to the batter. Fold them in gently (sak-kuri) to keep the texture light.
Pour the mixture into a parchment-lined pan. Bake in a preheated oven at 180°C (350°F) for about 30 minutes.
