Adjust the oven rack to the lower-middle position and the heat oven to 300 degrees.
Combine the salt, rosemary, thyme, oregano, fennel seeds, and pepper flakes in a bowl.
Tie the pork with kitchen twine at 1-inch intervals.
Transfer the pork to a large Dutch oven and season all over with the salt mixture.
Pour the broth around the pork.
Add the garlic to the pot.
Cover, transfer to the oven, and cook until the meat registers 190 degrees, 2½ to 3 hours.
Transfer the pork to a large plate.
Transfer the braising liquid to a 4-cup liquid measuring cup; add extra broth, if necessary, to equal 3 cups.
Let the pork and liquid cool completely, about 1 hour.
Cover and refrigerate both for at least 1 hour or up to 2 days.