Wrap pork tenderloin in plastic wrap and place in the freezer for 30 minutes. Remove plastic wrap and thinly slice or shave the tenderloin. Arrange pork on a platter or tray and set aside.
Place beef stock in a medium saucepan and bring to a simmer. Char the onions, shallots, and ginger, directly over a gas burner or under the broiler, about 5 to 6 minutes. Tie the charred vegetables, star anise, garlic cloves, and cinnamon sticks in dampened cheesecloth. Add the spice bag to the simmering broth. Simmer the liquid, covered, for 30 minutes.
When the beef stock mixture has simmered for 30 minutes, remove and discard the spice bag and bring the mixture to a rolling boil. Transfer the boiling stock to the fondue pot.
To serve: Use chopsticks or fondue forks pick up the pork and place in the boiling liquid, gently swirling until cooked, 1 to 2 minutes per bite. Serve pork with Sesame-Soy Dipping Sauce and hot cooked rice.