my mom was a star sio pao maker who even brought sio pao to the US when she visited my sisters for a vacation and ended up steaming batches by the dozen. she was the one who made the secret pork asado filling while my dad did the manual labor of kneading the dough. i swear, my dad absolutely hated that part of his vacation as he ended up doing house chores that would have been done by anyone from our household staff.
she never did other sio pao varieties, she only had pork asado and up to this day, i can not remember anything that can rival my mom's version. if my memory serves me right, she used the pork belly portion and had the meat cut up into small cubes after carefully taking off the skin. the fattier the pork, the better.
for all intent and purposes, pork asado is almost the same as adobo except that you add palm sugar for a very dominant sweet flavor to the dish. asado is even closer to humba minus the banana blossoms, black beans and star anise.
asado is an oily dish with a reduced sauce of soy sauce, vinegar, palm sugar infused with garlic and peppercorn which doesn't make a good sio pao filling. to keep the oil from separating from the sauce my mom adds dissolved cornstarch to thicken the sauce when the pork has turned a deep red. the consistency should be a very thick "paste" like mix that she can scoop using a standard measuring utensil and deposit it right in the middle of the sio pao dough. she carefully adds a slice of hard boiled egg before sealing the dough into a small ball ready to be steamed.
interestingly, humba may have been derived from the chinese stew "hong ma" or "hong ba" which literally means red meat. hong ba is traditionally served with cua pao and not the usual pata tim that we normally associate with cua pao.
you can probably conclude that there is a strong regional influence in a lot of asian dishes although my experience tells me that a lot of culinary flavors seem to have come from a chinese ancestor.
oh which reminds me, i had humba for lunch today. ang tsalap tsalap!