Mix 30 grams of warm water with active dry yeast and let the mixture sit for 5 minutes.
Mix all purpose flour, wheat flour, sugar, salt, milk, and oil together and then add the yeast mixture. Knead the dough for roughly 5 minutes until the dough is well combined and appears smooth on the surface. Let the dough rest for 20 to 30 minutes, depending on the room temperature. You may knead the dough by hand or using a mixer.
Shred cabbage and carrots in a bowl and sprinkle salt generously all over the mixture; let it sit for 5 to 10 minutes. Drain and squish out the excessive liquid. While waiting, soak a bundle of mung bean noodles in warm water.
Cut the mung bean noodles into one-inch length. Mix the processed cabbage and carrots with the rest of the stuffing ingredients and make sure they are well combined. You may microwave tiny bit of the mixture to determine how would you like to adjust the seasoning.
Divide the dough into 20 balls. Roll each dough into a round disk, which is a bit thick in the center and thinner on the edge. Put some stuffing on the center of the disk and then wrap it up. Make sure every bun is sealed on the top.
Let the wrapped buns sit in an enclosed warm environment for another 40 minutes. Then steam them for about 15 minutes.
You may freeze the steamed buns for up to 2 weeks for the best taste!