Smash the garlic and ginger lightly. Peel a yellow onion and cut into quarters.
Heat up the pot you’ll be making the soup in. Add the cardamom, cinnamon, cloves, star anise, peppercorns and coriander and heat for a minute or two, stirring, until you smell them. Remove the spices from the pot and put them aside. Add the smashed garlic and ginger, the quartered onion, lamb shanks and cover with water. The water should come about an inch above the meat. If you add too much water, the stock will be watery and not intense.