For the activator, add yeast to water at room temperature, and set aside for 5 minutes.
Cook the starter by adding flour to water, and then bring it to 65°C, set aside to cool to 7°C. Use this as a wet ingredient later.
Add all the wet ingredients and the starter to the activator and mix well.
Mix in all the dry ingredients, then bring the mixture together. If using a machine, keep the temperature low by using cool wet and dry ingredient.
Knead for 6 minutes, ensuring the dough's temperature does not increase above 28°C. If you use your hands, you should not need any flour and your hands, the table and the bowl should all be clean.
Mix in the butter and knead for another 2 minutes.
Proof for 40 minutes at 28°C.
Cut into bun size, either 30g each for small buns or 60g for normal commercial sized ones., proof for another 30 minutes.
Shape and incorporate whatever fillings and toppings desired, and egg wash with reserved egg.
Proof in a warmer environment at 38°C.
Bake at 200°C for 12 minutes until the bottoms of the buns are 2/3 golden brown in color.