Dry the pork leg roast using paper towels and rub salt all over then place on a roasting pan skin side up. Bake the pork in a preheated oven at 160C for 1 1/2 hours then let it cool.
Bake pork again in 180C preheated oven for 30 to 45 minutes or until skin becomes crispy.
Let the meat cool down on a wire rack then cut into bite sized cubes.
Sauté garlic and onion in a pot for a minute.
Add the cubed pork, bone, water, vinegar, Mang Tomas sauce, soy sauce, sugar, peppercorn, and bay leaves into the pot.
Bring the mixture to a boil and simmer for 45 minutes. Or until pork is tender enough to be broken down by a fork and the sauce is thick. If you find the sauce too thick, you can add water to help balance it out.
Flavor with fish sauce and freshly ground black pepper for seasoning.