In a large pot, add the beef shanks and 10 cups of water. Bring to a boil over medium heat. Skim off any scum or impurities that rise to the surface to keep the broth clear.

Once the scum has been removed, add the quartered onion and whole black pepper. Lower the heat to a simmer, cover, and cook for about 2 to 3 hours, or until the beef is tender and the bone marrow is soft. If using a pressure cooker, reduce the cooking time to 45-60 minutes.

When the beef is tender, add the fish sauce and onion leeks. Stir and simmer for another 5 minutes to allow the flavors to blend.

Add the corn pieces and quartered potatoes to the pot. Simmer for about 10-15 minutes, or until the potatoes are tender.

Add the quartered cabbage and bok choy leaves to the pot. Simmer for another 2-3 minutes, just until the vegetables are tender but still crisp.

Taste the broth and adjust the seasoning with salt and pepper as needed.

Serve hot with steamed rice, and enjoy your hearty Beef Bulalo!