Prepare the steamer
Fill a steamer or large pot with water and bring it to a gentle boil.
Mix dry ingredients
In a bowl, combine flour, sugar, matcha powder, baking powder, and salt.
Add wet ingredients
Add milk, vegetable oil, and vanilla extract to the dry mixture. Mix until smooth.
Prepare molds
Pour the batter into heat-safe cups or molds, filling them about 70%.
Steam the cakes
Place the cups in the steamer and cover with a lid. Steam on medium heat for 12–15 minutes or until a toothpick inserted comes out clean.
Cool and serve
Allow the cakes to cool slightly before serving. Optionally, top with sweet red bean paste or powdered sugar.