Two possibilities for cooking the shank: in a casserole dish or under pressure (Cookéo for example).
Arrange the knuckle in the cooking container of your choice.
Add the salt, peppercorns, bay leaves, coarsely chopped onion, the head of garlic just cut lengthwise and water.
Cook 45 to 60 minutes in the casserole dish or 20 minutes under pressure. Check that the meat is tender but still holding to the bone.
Set the shank aside and heat the cooking oil.
When the oil is hot, fry the knuckle until it becomes crisp on all sides.
Take out the knuckle from the oil and remove the excess oil with absorbent paper.
Cut into slices and serve with a sauce consisting of soy sauce and white vinegar (easily found in Asian grocery stores) in equal parts.