Prepare the veggie filling (can be done the day before):
Preheat a large wok or skillet. Add cooking oil. Add onion and saute until soft, about 3-4 minutes. Add shredded cabbage and stir fry for about 1 minute. Add vegetable broth and cover with a lid. Cook until the cabbage is soft, about 5 minutes or so
Uncover the lid and add carrots followed by seasonings. Stir to mix everything and continue to cook until liquid evaporates and the veggie filling is dry. Garnish with a chopped green onions. Have a taste and adjust seasonings to your liking
Let the filling cool down completely before wrapping. If preparing ahead, let it cool down completely and then cover and store in the fridge
Prepare carrot juice:
Place the carrots and water in a blender and blend into a juice. You will get roughly about 1 cup of juice. You may not need all of the juice
Prepare the dough with a machine:
Place the flour, instant yeast, sugar in a mixing bowl. If you are using a stand mixer, use a dough hook attachment. Add 1/2 cup of the carrot juice to start with. Add cooking oil. You may need to add more juice if the dough is still a bit dry. Add more teaspoon by teaspoon until the dough comes together and continue to knead for 10-12 minutes until the dough is very stretchy and smooth
Prepare the dough by hands:
Place the flour, instant yeast, sugar in a mixing bowl. Mix until you get a rough dough (it's not going to be smooth yet). Cover and rest it for 15 minutes. Then go back and knead it. You'll be surprised by how easier it is to knead it now. Knead until the dough is smooth and pliable, about 15-20 minutes. At any point during kneading, you can always stop and rest the dough if you find it hard to knead. This is to relax the gluten. Then go back to knead again and you'll be surprised by the difference it makes by just resting the dough before kneading again. It's easier for you too
Rest the dough:
Cover and rest the dough for 15 minutes. This is not to proof the dough. It shouldn't double in size. This is to relax the gluten for easier shaping and rolling the dough
Wrapping:
Divide the dough into 12 equal portions. Lightly dust the work surface with some flour. Flatten the dough with your palm and then use a rolling pin to roll it out to form a circle about 4-5 inches, with a slightly thicker middle part. This is to support the weight of the filling. Don't roll the dough too thin. If you roll the dough too thin, the filling might make the steamed buns "wrinkle" later when you steam
Scoop about 1-2 Tbsp of the filling onto the middle of the dough. Gather the sides to enclose the bun and pinch to seal the buns. This can be the pattern for the bun or if you flip the bun so the seam side is down, you will just have a smooth round steamed buns
Cup the dough with both palms and move the dough in a circular motion to shape it taller. This part is important so your steamed buns come out tall instead of spreading to the side after steaming
Steaming:
Most likely your steamer won't be able to accommodate steaming all buns at one go, unless you have something like this 3-tier food steamer (which I like to use a lot!). You may need to steam in 2-3 batches, which means, the rest of the batches will sit longer and continue to proof while waiting for the steamer. Not good for the buns! Here's what you can do: Make sure the cover them with plastic wrap and then place them in the refrigerator to slow down the yeast activity or halt it all together until they are ready to be steamed
Bring the water in your steamer to a boil. Wrap the lid of your steamer with a kitchen towel to prevent moisture dripping back on the steamed buns as this will create "burn" spots
LOWER THE HEAT TO MEDIUM . Place the buns in there, leaving about 1-inch space in between. Cover with a lid and leave about 1/4-inch gap to let some steam escapes. This helps to prevent wrinkle on the steamed buns. Steam on medium heat for 10 minutes
After steaming, turn off the heat. DO NOT OPEN THE LID of the steamer. Let the buns sit there for 1 minute like this. The buns will not sink or wrinkle due to the sudden change in temperature
Cooling:
Remove the buns to a wire rack to let them cool down. This is to ensure the bottom of the steamed buns will not be wet and soggy
Notes
You can also replace all 300 gr of all-purpose flour and 60 gr wheat starch/corn starch with cake flour or premixed Hongkong/Vietnamese bao flour and omit the wheat starch/corn starch.