Blanch the pork legs with boiling water and dry off. Blanch them again after they have cooled off.
Heat a dutch oven or a wok with a lid. Add the vegetable oil and cook the garlic, ginger, pepper, cinnamon and star anise until they release the aromas.
Add the pork pieces and cook all over until the skin gets a good colouring.
Add enough water to cover the pork and add the fish sauce, soy sauces and palm sugar.
Bring to a boil then reduce to a simmer and cover.
Cook for at least 90 minutes. Check the seasoning of the reduced sauce and season to taste.
Remove the pork from the wok or Dutch oven and cover with foil to keep it warm while resting.
Strain the stock and return to the heat to reduce to taste.
Serve family-style on a tray and pour over the sauce and sprinkle the coriander leaves over the top.
Serve with jasmine rice and stir-fried bok choy.