Mix and knead the dough until smooth, then roll it into long strips and cut small sections. Use a little flour and water to knead white dough, this does not need to add yeast. Knead the yellow dough into an oval shape and flatten it slightly. Roll out the white dough into small thin strips. Use chopsticks to poke holes in the white strips and press them in. Brush with a little cocoa powder and spread. Place a greaseproof paper on a pot of cold water and let it rest for 10 minutes Turn the heat on high to medium for 10 minutes and let it simmer for 3 minutes to uncover.