Start by steaming the salted egg yolks for 20 minutes or until they turn a bright orange color, then use the flat side of a large cleaver to mash the yolks.
Repeat the mashing until you have fine crumbs or a paste.
Mix the salted eggs, butter, icing sugar, custard powder, milk powder and evaporated milk together in a bowl until well combined.
Put the mixture in the fridge for 20 minutes to firm up.
Take the salted egg mixture out of the fridge and form them into balls, roughly 3cm (1.2") wide. Refrigerate them as you make the bread.
Sift the flour in bowl and make a well in the center. Add yeast, caster sugar and baking powder into well, then pour the milk and water in.Note: Add the liquids in a little bit at a time while mixing it with the yeast, caster sugar and baking powder.
When all the liquid has been added, work it into the flour until it forms a dough. Knead for 20 minutes.
Pour the oil in and knead the dough for 10 minutes or until smooth and waxy, then cover it with a clean towel to rest for 30 minutes.Note: If you find it too dry, add some water. Likewise, if it's too wet then add some flour until it reaches a dough consistency.
Meanwhile, cut baking paper into squares approximately 10cm x 10cm (4" x 4"). Alternatively, use cupcake liners.
After the dough has risen, take it out and knead for 2 minutes.
Divide the dough into approximately 11 portions and cover with a towel to prevent drying out.
Roll the ball until flat, roughly 5mm (0.2") thick and 12cm (4.7") wide.
Take the filling out of the fridge and place one in the center of the flattened ball.
Use your hand to wrap the dough around the filling while leaving an opening at the top.
Use your thumb and index finger to seal the opening by bringing the ruffled parts together.
When turned upside down, it should look like a sphere.
Twist the seal until closed and push it in to flatten. If there is excess dough, you can tear it off before flattening.
Place the ball on a baking paper square, sealed side down.
Let the baos rest for 10 minutes before putting them in the steamer to cook.
Steam the buns on a medium heat for 10 minutes.
Serve immediately as is!