Chinese cabbage soup
Wash the pak choi thoroughly under cold running water, rinse and drain. Pat dry with kitchen paper. Trim the stems from the pak choi, and shred the leaves.
Heat the stock in a large heavy saucepan. Add the pak choi and cook for 10–15 minutes.
Mix together the vinegar, soy sauce, sugar and sherry in a small bowl.
Add this mixture to the stock, together with the chilli. Bring to the boil, reduce the heat and cook for 2–3 minutes.
Blend the cornflour with 2 tablespoons water to form a paste, and gradually stir into the soup. Cook, stirring constantly, until it thickens. Cook for a further 4–5 minutes, then ladle the soup into warm individual serving bowls and serve immediately.