Trim any major layers of fat off your pork shoulder, but don’t try to get it too lean; you’ll need the fat later on. Cut your pork into chunks roughly 1 ½ to 2 inches.
Put the pork in your big, heavy skillet—you want a single layer, but the pork cubes can be very close together. Cover with water, add the salt, if using, and put over a burner set to medium-high heat. Bring water to a boil, then turn burner down to low—you want to keep the water barely simmering.
Now let your pork cubes simmer, about 3-4 hours. (If you happen to be wandering through the kitchen, turn the cubes over once or twice.)
Let your pork simmer until the water has completely cooked away. Continue cooking, letting the pork cubes brown in the fat that has collected in the bottom of the skillet. When they’re crisply brown, they’re done.