Spray the salted egg yolks with spirit wine and let bake in an oven set to 170 degrees for 8-10 minutes. In Chinese cooking, we love to use our hard spirit to remove any raw taste. Then, mash and sift the salted egg yolks. You can find it is super fluffy at this stage. It can be super comforting for me, but you need to push hard to finish this step.
Melt the butter with hot water in a bowl. Then add granulated sugar, milk powder, custard powder, and whole milk and stir evenly.
Then add the sifted salted egg yolk, and stir evenly again. Place it in a pot filled with boiling water and stir it to melt it until there are no particles.
Strain to remove any possible bumps and freeze it for 30 minutes to an hour until it becomes a slightly hard solid.
For the dough
Add yeast, sugar, vegetable cooking oil, and milk to the flour, knead until the dough becomes smooth and elastic.
Cover the dough with a large bowl. Rest for around 10 minutes.
Assemble
Now transfer the dough to a lightly floured board. Knead it again until achieve a smooth Then roll into a long log; cut the log into 12 equal portions.
Take out one flour portion, compact it slightly, and roll it out into a round crust of 8 to 10 centimeters in diameter. Try your best to make the edges thinner than the center. You can use a rotating rolling method or slightly press the edges with your fingers.
Place a filling portion on a round wrapper and seal completely. Then flip the bun and shape it into a perfect round bun. Repeat the process to finish all the bread.
Steam the buns
Rest the buns covered and wait for around 1 hours to 3 hours (depending on the room temperature). In summer, when the room temperature is around 28 degree C. It takes around 1 hour. If the it drop under 20 degree C, you may need at least 3 hours or even longer
Set up your steamer and place the buns in. Steam for 8 minutes is enough after the water is boiled. Let it stand for 5 minutes before opening the lid.
Notes
Be careful when eating the buns because it might be quite hot.
The bun can turn harder after cooled, reheat before serving next time.