Rinse the sweet potato, slice into 1 cm rounds, and soak in salt water to keep the color from changing. (Salt not listed).
I used homemade tsubu-an. Use whatever anko is available.
In a large bowl, add dry ingredients and hot water while mixing with a fork. (Be careful not to burn yourself.)
Although it's hot to handle, form the dough into a ball. Knead until the consistency is smooth, wrap with plastic wrap to keep it from drying out, then let sit for about 15 minutes.
Take out as many sweet potatoes as you will need, rinse off the salt, and wipe the excess water with paper towels. Spread a generous amount of anko on top of each slice.
Remove enough dough to wrap around a slice of sweet potato, and using your palm and fingers, flatten and stretch into a circle. (You can also use a rolling pin, if necessary.)
Use both hands to wrap the dough completely around the anko and sweet potato.
Line the steamer with a cloth and steam for about 30 minutes on high heat (or until a skewer lightly inserted into the sweet potato pierces though completely.)
Wrap in plastic wrap as soon as the residual heat has dissipated. It also tastes delicious while still hot.
Story Behind this Recipe
I wanted to see if I could make these Imokoi, even though I live outside Japan. Recently, at the supermarket, I can find sweet potatoes that are similar to the ones sold in Japan.
Feel free to change the thickness of the sweet potato slices, peel, or increase the amount of glutenous rice flour in relation to the plain wheat flour. Take care when handling the hot water. A dry dough can be tricky to wrap around the sweet potato, but it's easier to handle, since it doesn't stick to your hands. Conversely, a softer, moist dough is easy to wrap, but it sticks. The recipe makes a slightly dry dough.