Lay out a large piece of parchment paper on the work surface.
Take the plain dough and roll it out to a size of about 9" by 15."
Cover the plain dough with another piece of parchment paper and move it aside.
Repeat with the matcha dough, until you have another dough rolled out to about 9" by 15."
Decide which dough you'd like on the exterior (either matcha or plain). Place that dough on the work surface.
Spray the top of the dough with water (this will help the dough stick together).
Lay the second dough on top of the first dough. Pat the dough and smooth it out evenly, rolling it if need be.
Then, from the bottom side of the long edge, roll up the dough into a coil.
Cut the dough into 8 even pieces.
Place each mantou onto a square piece of parchment paper and transfer to a bamboo steamer. Cover the steamer with the lid.
Add about 4 C boiling water to the pot that you'll be using to steam the buns and place the steamer rack over top.
Let the buns proof for 20 minutes.
Turn the heat onto high heat and steam for 15 minutes.
After steaming, leave the buns in the steamer for 5 minutes before cracking open the lid slightly to let the steam escape. Once the steam has completely dissipated, remove the lid.
Serve warm, with condensed milk if you wish.