Place the beef shanks in a large, heavy-bottomed pot and pour in enough cold water to fully submerge the meat. Bring the pot to a rolling boil over medium-high heat. Once it reaches a boil, drain the beef and rinse it thoroughly under cold running water to remove any scum and impurities. Discard the cloudy water and rinse the pot clean.

Return the cleaned beef shanks to the pot and again cover with fresh cold water. Bring to a gentle boil, diligently skimming off any froth or impurities that rise to the surface. Once the broth is clear, add the quartered onion, fish sauce, and whole peppercorns.

Lower the heat, cover the pot partially, and allow the broth to simmer at a bare bubble for about 1½ to 2 hours. The beef should become tender and flavorful, yet still hold its shape without falling apart.

When the meat is tender, add the halved corn pieces and continue to simmer for another 10 to 15 minutes, until the corn is cooked through and sweet.

Introduce the pechay and green onions to the pot, letting them wilt and soften gently in the broth for about 2 to 3 minutes.

Season the broth with salt according to your preference. Serve the Bulalo piping hot, accompanied by a small bowl of fish sauce mixed with calamansi juice and chopped Thai chili peppers for dipping.