Soak shiitake mushrooms in boiling water for 5 minutes until they plump up. Strain the soaking liquid into a bowl and reserve. Set mushrooms aside for later.
Bruise ginger and garlic with the flat of your knife or in a pestle and mortar. Add to a heavy-bottomed pot or pressure cooker. Coarsely crush peppercorns and add to the pot.
Cut each chicken wing into 3 or 4 pieces and add to the pot. Turn the heat on and fry the chicken with the ginger and garlic until chicken pieces are browned and starting to cook, about 7 - 10 minutes.
Add cinnamon stick, star anise, spring onions, reserved mushroom liquid and salt. Pour 1 litre of water and cover and cook over a low heat for anywhere between ½ hour to 2 hours in a pot (longer the better) or ½ hour in a pressure cooker.
Strain the stock into a bowl, pushing down with a spatula to get maximum flavour. Use right away, refrigerate for up to 1 week or freeze for up to 3 months.
Once the chicken pieces are cool enough to handle, shred the meat with your fingers and use in your dish. Similarly, slice the shiitake mushrooms and add to your dish. If not using right away, freeze for later.