Slice the pork and trim away most of the fat. Dice both the lean meat and the fat into 1/2-inch cubes; set the diced fat aside. In a heavy pot over a hot flame, cook the lean pork with the water, stirring until the water is gone and the meat begins to brown. Add onion & garlic, and stir constantly until the onion becomes transparent.
Reduce heat to a simmer and add tomatillos & canned chiles (be *sure* to drain the tomatillos before crushing; the water they are packed in is too salty). Cover the pot and simmer slowly for about an hour, stirring occasionally to prevent sticking. Meanwhile, render the diced pork fat into cracklings by sautéing in a skillet over medium heat until the pieces are brown and crispy. Drain and salt the cracklings and set aside; save the lard for any other dish where you want some high-quality cholesterol stuff. After an hour the chile verde should be pretty juicy but not watery. Add a little water if it's too dry. Add salt & pepper to taste, and if you want it hotter, add your fresh chiles now. Cover and simmer again for at least half an hour. The longer the better. To serve, sprinkle with chopped cilantro (if used), chopped jalapenos and, the cracklings. Serve with Spanish rice, tortillas, black beans, and ice-cold beer.