Pour 3 to 5 cups of water in a large cooking pot and add the pig head. Let the liquid boil. Cook covered for 10 minutes. Discard the water afterwards.
Pour around the same amount of water in the pot and add lemongrass, onion, and laurel leaves. Cover and boil the pig head with all the newly added ingredients for 60 to 90 minutes. You can turn the head over in the middle of the cooking process.
Discard everything except the pig head. Let it cool down. Create cross-hatch incisions on the face of the pig using a sharp knife. Rub salt all over the head and let it air dry for at least 3 hours (the longer the air drying process, the better the result).
Rub oil all over the pig head and arrange it inside a turbo broiler. Broil for 1 hour at 400F.
Meanwhile, make the lechon sauce by heating 3 tablespoons of oil in a cooking pot. Add the sliced liver and saute for 3 minutes.
Remove the liver from the pot and place inside the blender. Add water and then puree. Set aside.
Heat the remaining oil (add more if needed). Saute garlic and onion until the onion softens. Add laurel leaves and whole peppercorn. Continue sauteeing for 1 minute.
Pour the liver puree into the pot. Stir and let boil.
Pour vinegar and soy sauce. Allow the liquid to reboil before stirring.
Add brown sugar and stir. Turn the heat off and pour the entire mixture back into the blender. Puree for 1 minute.
Pour the puree back into the cooking pot. Let it boil.
Season with salt and add breadcrumbs to thicken the sauce.
Arrange the crispy pig head on a serving plate and serve with lechon sauce on the side. Share and enjoy!