Brown the pork. Heat enough oil to coat the bottom of a large pot or wok over medium-high heat. Brown the pork leg on all sides for about 5 minutes, then remove.
Make the spice base. Pound the garlic, coriander root, and black peppercorns into a rough paste. In a large pot, stir-fry the paste with the cinnamon stick, star anise, and soaked shiitake mushrooms until fragrant.
Build the broth. Add the palm sugar and cook until it begins to caramelize. Stir in the water, Chinese five spice powder, light soy sauce, dark soy sauce, and salt.
Braise the pork. Return the pork leg to the pot, cover, and simmer over low heat for about 3 hours, turning the pork once or twice during cooking.
Add the eggs. If using, add the hard-boiled eggs during the last 30 minutes of cooking so they absorb the flavorful broth.
Serve. Blanch the choy sum, Chinese broccoli, or bok choy until just tender. Serve the braised pork with steamed jasmine rice, the vegetables, braised eggs, pickled mustard greens, and my spicy vinegar dipping sauce.