1. Put all the ingredients in the dough except butter into a basin and knead until the dough becomes stiff (at this time, the dough surface is smooth, and a film can be pulled out by cutting a small piece of dough, but the film is not firm enough).

2. Cut 20 grams of butter into small pieces and put it in a basin.

3. Knead into an expanded state (the state at this time is: take a small piece of dough and open it by hand. The dough can form a light-transmitting film, but the strength of the film is average. After being punctured by hand, the fracture edge is irregular and the dough is in the expansion stage)

4. Put the kneaded dough into a basin, cover it with plastic wrap and put it in a warm place for basic fermentation.

5. Ferment to 2 ~ 2.5 times the size of the original dough, and poke a hole in the dough with your finger dipped in flour, which will not retract, indicating that the fermentation is complete. (I wandered around Weibo again this time, and the fermentation was a bit overdone. What a good lesson! )

6. Knead the fermented dough for a while, exhaust the air in the dough, divide the dough into 8 parts on average, round the dough, and relax at room temperature 15 minutes.

7. flatten the loose dough, turn it over, wrap it in a small piece of butter and tighten the mouth to avoid bursting in the middle of baking in the oven.

8. Put it in a baking tray for final fermentation (beat the oven for a while, put your hand in it to feel hot, put a bowl of hot water in the oven to increase humidity, and put the baking tray in the oven for final fermentation).

9. When the dough is fermented to twice its original size, take out the surface and brush it with egg liquid, and sprinkle with sesame seeds. Bake in the middle layer of the preheated oven at 180℃ for about 15 minutes. If the later color is too dark, it can be covered with tin foil. You can only eat it after it is taken out of the oven and cooled.