Make the prawn stock by sautéing the prawn shells in a non-stick pan for 2 minutes. Add the shallots, garlic and parsley and sauté for a further 5 minutes.
Add the water and bring to the boil, then cover and simmer for 20 minutes. Pass through fine muslin, then season to taste.
Start the remainder of the recipe by sautéing the spring onions and ginger i