Add 60g glutinous rice flour, 60g regular rice flour, 30g wheat starch, 30g sugar, 220g milk, and 30g condensed milk to a large mixing bowl, whisk until well combined.
Place a strainer over a heat-resistant bowl, pour the mixture through the strainer to the bowl to filter out any lumps. Cover the bowl with plastic food wrap, use a toothpick to poke about 16 holes on the wrap.
Steam the mixture over high heat for 25 minutes until there is no liquid in the bowl.
Take the bowl out from the steamer, remove the plastic wrap, make some cuts into the dough to make it cools down faster. Put 30g butter on top of the dough, wait until the butter is melted and the dough is cooled down a bit (warm but not too hot to be handled).
Transfer the dough with the butter to a large kneading bowl or a nonstick kneading mat, put on food safe rubber gloves, knead the dough for about 5 minutes until it has absorbed all the butter in and turns smooth. Optionally, divide the dough into two equal portions. Add 1/3 tsp of matcha powder to one them, knead the dough until the color is evenly distributed.
Roll each dough into a rope about 10 inches long. Twist the two doughs together and roll the twisted dough into one rope.
Cut the dough into 18 pieces, each piece should weigh about 20g. Roll each piece into a ball, then flatten into a round wrapper (about 4 inch diameter). Cover the wrappers with plastic food wrap to prevent them from drying.