Step 1Place the pork, onion and garlic in a large pot and cover with water. Bring to a boil, then reduce the heat to medium and simmer, covered, for 2 hours, checking after 1 hour and adding water if necessary to cover the meat.
Step 2After 2 hours, add the salt and simmer for 30 minutes to 1 hour more, until tender.
Step 3Carefully remove the meat from the pot and place on a large platter to cool. Skim the fat from the stock and discard. Reserve the stock for use in the sauce and the masa. Cut the pork butt into 1-inch cubes.
Step 4Meanwhile, prepare the chili sauce and then prepare the masa.
Step 5Combine the cubed pork and the chili sauce in a large bowl.
Step 6To assemble the tamales, spread one-third to one-half cup masa on the smooth side of a corn husk. Spread the filling onto the top third of the husk, leaving one-half inch of the husk free of filling; the filling should be one-fourth inch thick. Spoon about one-fourth cup pork and sauce onto the center of the tamale. Place one olive at the end of the large end of the husk so that it will sit on top of the finished tamale.
Step 7Fold the long sides of the tamale over the center, forming a bundle, then fold up the bottom to make a packet that is open on top. Repeat with the remaining tamales.
Step 8To steam the tamales, fill a large pot that has a steamer basket insert with 4 to 6 inches of water. Leaving out the insert, heat the water to a boil. In the meantime, loosely fill the steamer basket with the tamales, placing them along the sides of the basket with the tamale opening faceup. (Steam needs to be able to come up between the tamales for them to cook evenly. Cook the tamales in batches if necessary.) Steam the tamales for 1 hour. Pull one tamale out and unroll. If the masa rolls cleanly off the husk and is set, they are done. Cook an additional few minutes if necessary.