Wash the sweet potato well, and cut into 1 cm cubes with the skin on. Place in a heatproof dish, loosely cover with plastic wrap, and microwave for about 5 minutes at 500 W.
Beat the egg in a bowl, add the milk, and mix. Add the remaining ingredients, and continue mixing. (Set aside some for decoration.)
Line the pan with cupcake cups, and pour in the batter evenly. Top with the sweet potato. If the cups are strong enough, you don't need to use the pan. You can also use ramekins or pudding cups instead.
Bring water to a boil and place the pan in a steamer. Steam for about 15 minutes over a high heat. Insert a bamboo skewer, and if it comes out clean, they're done.
Story Behind this Recipe
I created this because I felt like eating sweet potato steamed bread.
Wrap the steamer lid with a large cloth and tie the top of it. (This is to prevent condensation from falling on the steamed bread.)