Five Spice Pork Rillettes

Preheat oven to 325 °F with rack in lower third. Mince and mash garlic with five-spice powder, 1 tablespoon kosher salt, and 1/2 tsp pepper. Rub onto pork and fatback in a 5-quart heavy pot. Wrap parsley, bay leaf, and halved scallions in cheesecloth and tie with string. Add to pot with pork, water, and 1/3 cup Sherry and bring to a boil. Cover and braise in oven until meat is very tender, about 3 hours. Boil carrot until crisp-tender, about 4 minutes. Stir in chopped scallion and cook 1 minute. Drain and cool slightly. Drain pork mixture in a large sieve set over a bowl, reserving liquid. Finely shred meat and lightly mash fatback with tines, transferring both to a bowl. Skim and reserve fat from liquid. Stir 1/2 cup liquid into meat with vegetables, remaining tablespoon Sherry and 1/2 teaspoon kosher salt, and 1/2 tsp pepper. Cool. Transfer to terrine, pressing lightly. Top with 1/4 inch of fat. Cool, then chill 8 hours. Serve at room temperature.