1. The purple sweet potato is peeled and cut into pieces and steamed on the steamer, crushed with a fork into a puree, and poured in lemon juice to instantly change the purple to light purple.
2. Mix it with high flour, water, and yeast, knead it into a smooth purple potato dough by hand, and ferment it.
3. Mix high powder, sugar, yeast, and water, knead it into a smooth white dough, and ferment it.
4. The purple sweet potato dough is fermented to twice its size.
5. The white dough is fermented to twice its size.
6. Knead the two doughs into strips, divide the dough, knead and let stand for 10 minutes.
7. Take the white dough and roll it flat with a rolling pin, wrap the purple sweet potato dough, and place it with the mouth facing down.
8. Use a knife to make a cross on the surface of the dough.
9. Let it stand for 20 minutes and then let the pot on cold water, turn to medium heat and steam for about 8 minutes after the high heat is brought to a boil.
