Mix all of the ingredients from the tangzhang into a small saucepan and heat gently. Whisk for about 3 minutes until there are no more lumps and the whisk leaves lines on the bottom of the pan. Let this cool.
Mix the rest of the ingredients together with the cooled tangzhang and knead until a smooth elastic dough is formed. If the dough is too sticky add a bit of flour until it is smooth.
Roll into a giant ball and place in a lightly floured bowl. Lightly dust the top with flour and cover with a tea towel or plastic wrap. Rest for about one hour.
After about an hour the dough should have expanded slightly but not doubled. Lightly press the air out and begin shaping into 8 smaller balls. Attach them together on a parchment lined baking tray and lightly dust with flour. Cover with plastic wrap and let rise for 40-50 minutes.
Preheat the oven to 175C/350F. Lightly brush the dough with an egg wash (1 egg with a splash of cold water mixed in). Bake for about 23-35 minutes or until nicely golden on top and a thermometer reaches 87C/190F.
Transfer to a resting rack and let cool for ten minutes. These buns are amazing hot out of the oven with a little butter and crunchy sea salt. They also makes an incredible egg sandwich the next day with a little fried egg.