Add 9g yeast and 210g water in a bowl. Add 350g High-gluten flour and 15g fine sugar in the bowl and mix well. Then, put it in the refrigerator and fermented it until the dough expands to the center of the highest point and falls slightly, and the interior is honeycombed.
Add the dough, 150g High-gluten flour, 6.5g salt, 55g sugar, 15g milk powder, 6g yeast, 50g whole egg liquid and 88g milk in a blender. Stir it under high speed until the dough becomes smooth.
Add 35g soften butter into the dough and continue to stir it under middle speed until the butter mixes well with the dough. Turn the speed level up and stir the dough under high speed until you can pull the dough out of the transparent film. Transfer the dough on a workbench and roll it.
The dough was placed in a container and wrapped in plastic wrap and allowed to continue to ferment for half an hour in an environment of 25-28 degrees.