1. Wash the purple sweet potatoes, steam them, cool, peel and chop.

2. Add plain flour and baking powder to the purple sweet potato. , yeast powder, cooking oil, white sugar and appropriate amount of water to form a dough (water should be added slowly, because purple sweet potatoes have moisture). Let it sit for 20 minutes.

3. Take about 30 grams of dough, roll it into a dumpling wrapper, and use. Mold out the shape of the donut, take out the middle piece, and then take the last 50 grams of dough and shape it into a ball and press it with a hollow dough piece on top to serve as the top. Take at least 30 grams of dough and shape it into a long and thin strip. Use it as a butterfly knot under the ball. Let it sit for 10 minutes.

4. Just steam it for 10 minutes in the same way as steaming steamed buns.