Add the flour and milk to a pan over medium high heat and whisk continuously till it thickens. Scrape into a bowl and leave to cool.
Dough
Add tangzhoug, strong bread flour, yeast, sugar, egg and milk to bowl of stand mixer and mix on medium low for 10 minutes.
Add salt and mix in, then add butter slowly with mixer running until fully mixed in.
Continue to knead in stand mixer on low for 15 - 20 minutes until glossy and until the window pane test method works. (See notes).
Gather dough up and add to a greased bowl. Cover with damp cloth and leave to prove for 1.5 - 2 hours.
Lightly flour your work surface and divide dogh into equal pieces - around 70 - 90 g. (9 buns).
Roll each peice out flat and fill with a mixture of your choice.
Cover lightly with greased cling film and allow to rise for 1 hour.
Make the egg wash by whisking the egg and milk together. Paint over the buns and sprinkle with sesame seeds if you like.
Bake at GM 5, 215 °C for 12 - 15 minutes.
Notes
Storage - These last well at room temperature for 2 - 3 days. They freeze well for a month.Window Pane - Once you can stretch the dough with your fingers without it tearing, it is ready. Enough gluten has developed in the dough for it to begin proofing. This is called the windowpane test. If the dough tears, it means you need to knead a little more.Stuffing - You can use any stuffing of your choice.