1. Raw materials: all-purpose flour, sugar, old dough starter, warm water, edible alkali, lard, purple sweet potato.

2. Prepare a piece of old dough starter, an appropriate amount of flour and a purple sweet potato.

3. Dissolve the old dough starter with warm water, add warm water to the flour, and put the sugar into the bread machine.

4. Add a little lard, knead it into a smooth dough, and put it in the refrigerator to ferment overnight.

5. The next morning, add edible alkali to the fermented dough, deflate it, knead it smooth again, and prepare a purple sweet potato.

6. Cut the purple sweet potato into small pieces.

7. Roll the dough into a 1cm thick piece.

8. Layer the purple potato dices.

9. Roll up from one side into a long strip.

10. Cut into small uniform pieces.

11. Gather into a circle again.

12. Pour cold water into the pot and put it into the steamer to ferment again for 20 minutes.

13. After 20 minutes, turn on the fire. After the steam comes out, steam for 15 minutes and then steam for 5 minutes.