Wash the sweet potatoes thoroughly and peel them.
Boil or steam the sweet potatoes.
Mash the boiled sweet potatoes and mix with sugar and salt.
Make a dough using flour, yeast, sugar, milk, and butter.
Divide the dough into appropriate portions, add the sweet potato filling, and shape into bread.
Bring water to a boil in a steamer, place the breads in, and steam for 15–20 minutes.