Combine dry ingredients for both types of dough in 2 separate mixing bowls, mix well. Add in milk, and mix into a dough. If the doughs are drier, add in more milk, ½ tsp at a time, until it reaches the consistency as shown in the video (all flour just comes together to form a dough, it is not sticky). (Reminder: Prepare both doughs at the same time so that the proofing time is consistent.)
Add in corn oil, and knead until well blended.
Cover Matcha dough with a bowl to prevent it from drying out.
Use a stand mixer with a hook attachment and knead milk dough over “speed 2” for 5 minutes until a smooth dough is formed. Shape dough into a ball, cover, and set aside to rest for 6-7 minutes. Knead Matcha dough over “speed 2” for 5 minutes, until a smooth dough is formed. Shape dough into a ball, cover, and set aside to rest for 6-7 minutes. (Reminder: Knead each dough for 6-7 minutes if do it manually, lightly coat the palm with flour whenever the doughs are sticky.)
Put the rested milk dough on a non-stick baking cloth, and roll it out into thin flat dough (cover the rolled dough to prevent it from drying).
Put the rested Matcha dough on a non-stick baking cloth, and roll it out into thin flat dough.
Brush the rolled Matcha dough with some water, put rolled milk dough on top of rolled Matcha dough, and roll out to left and right to help both doughs stick together.
Remove the baking cloths, put the dough on a non-stick silicon mat (with milk dough at the bottom), and roll out into thinner dough. Flatten the end where rolling starts. Brush with some water while rolling up the thin dough into a rod shape. (Reminder: Don’t brush the whole piece with water at one time as the dough will become soft when it starts to absorb the water and makes it difficult to be rolled up. Brush a small part at one time, then roll up immediately.)
Cut into 8 portions using a serrated knife (for a nicer cut), and put each onto a piece of paper.
Bring 500 ml of water to the boil in a steamer, off the heat, then add in 1 Litre of plain water.
Arrange mantou dough in steamer racks, put over warm water, cover, and proof for 20 minutes. (Reminder: Using a bamboo steamer to steam will prevent condensation water from dripping onto mantou, thus yielding a prettier bun.)
After proofing for 20 minutes, turn to high heat until water is boiling (about 3 minutes), then reduce to medium heat and steam for another 15 minutes.