In a large bowl, combine the pork with the garlic, brown sugar, fish sauce and green onion. Mix thoroughly to ensure even distribution of the seasonings. The best way to do it is just to get in there with your hands and massage the pig. Time permitting, let the pork marinate for 20 minutes or so to allow the seasoning to penetrate the meat.
In deep skillet or pot, heat 2 Tablespoons of a neutral flavored oil over medium high heat and sear the pork, 4 or 5 pieces at a time (don't want to crowd the cooking surface) until the fatty bits get a rich, dark, caramel color, 2 to 2.5 minutes per side. This is one of those rare instances in which you could actually put the seared pork back into the bowl with the uncooked pork without worrying about contamination because all of it is going back into the pot to cook for a long time.
After the pork is seared, add the onions into the pot and saute until they just begin to become translucent, about 2 minutes. This quick saute develops the flavor of the onion and helps it hold some shape during the long simmer.
Put the pork back in the pot, and increase the heat to medium high. Add the water, soy sauce and vinegar, stir to ensure they get evenly distributed, and bring to a gentle boil (i.e., the liquid is bubbling gently and consistently but not so actively that it splatters).
Reduce the heat to medium low and cover the pot. Simmer 45 to 50 minutes, stirring every 15 minutes or so to ensure that the meat gets evenly seasoned and cooked. Because heat accumulates, watch for signs that it's getting too high (the aforementioned splattery bubbling) and adjust back down if that happens.
At this point, the meat should be fork tender. If not, cover and simmer another 5 minutes or so.
Once the meat is fork tender, uncover and reduce the heat to low. Simmer another 15 minutes to reduce, thicken and further caramelize the braising liquid. Stir every 5 minutes to further ensure even seasoning and cooking.
If you refrigerate the leftovers, you'll find that the braising liquid becomes gelatinous due to the collagen from the pork. Just give it a warming on the stove or a zap in the microwave, and it's back to its saucy goodness in no time.
Enjoy!
