Add water into a container with a tight fitting lid (that's also microwave-safe). Add the finely chopped sweet potatoes.
Drain the water, then add fresh water (just enough to soak the sweet potatoes). Cover the container lightly and microwave for 4 minutes at 500 W.
Mix all ★ ingredients with a whisk.
When the potato is done, drain the water (take care not to burn yourself!). Add the mixture from Step 3 and mix lightly.
Lightly cover with a lid (as if you're only putting it on top! Do NOT cover tightly). Microwave for 2 minutes at 500 W. Steam for another minute to finish.
Use a chopstick and peel when you're taking it out from the container.
Here's how thick and fluffy it becomes if you use a smaller container and double the measurements. Microwave for 4.5 minutes at Step 2, and 3 minutes at Step 4.
Another update: If you make it with this container that's available at a 100 yen store.
Story Behind this Recipe
At first, I microwaved sweet potatoes as is, and they were too tough. So, I tried it again with water! The result was a delicious cake with fluffy sweet potatoes. It's a good snack for my 1 year old son who's allergic to dairy, and now it's our autumn special dessert. Also check out "Banana Steamed Bread" (Recipe ID: 2044585).
-Just place the lid on top when you're microwaving in Steps 2 and 5. Don't close it tightly. -I made these thin for my kids to eat, but you could use a small container to make it thick and fluffy. -In that case, adjust the microwaving time.