Using a boning knife (or similar), insert the knife just under the silver skin and slice all the way through the side until all the silver skin is removed.
Make 10 deep incisions in pork loin. Stuff garlic cloves in the incisions.
Sprinkle the pork loin all over with salt and pepper.
Heat vegetable oil in a large Dutch oven. Place pork loin garlic side down and allow it to brown for 3 to 4 minutes. Flip the pork loin over and brown the other side for another 3 to 4 minutes.
Add cinnamon stick, star anise, and cloves. Drizzle dark soy sauce over the top of pork loin.
Pour water into the dutch oven and bring to a boil. Reduce heat to medium low, cover, and simmer for 1 hour 30 minutes. Half way through, flip the pork loin once.
When done, remove pork loin and whole spices from the dutch oven. Cover pork loin with aluminum foil to keep warm.
Pour cornstarch mixture into the dutch oven and let it come back to a boil. Cook until thick and bubbly. Turn off stove.