In a word, magic.
1. Cut the pork into 2-3 inch chunks and put in a large heavy-bottomed pot. Add the remaining ingredients and bring to a boil. Reduce the heat to low/medium, cover and simmer for two hours, until the pork is tender and the fat is liquefying.
2. Keep in mind that throughout this cooking process it will look downright unappetizing. At the beginning it's like the brown sea-foam at low-tide. After two hours simmering it smells good, but looks gray and dingy. This is normal, stay the course! It's only until the last 15-20 minutes of cooking that it starts to reveal itself.
3. Uncover and boil the pork until the liquid evaporates and the meat browns and begins to crisp. Stir occasionally to keep the meat from sticking to the pan. This should take about an hour. At 20 minutes left to go, keep stirring regularly until the fat renders and the meat falls apart and crisps up.
Serve with corn tortillas, avocado and some shredded cabbage tossed with lime, cilantro, and pickled red onion. These can be made a day or two ahead. Simply crisp them up in a nonstick skillet when you're ready to serve.