Sour and Spicy Prawn Soup

This is a classic Thai tom yum, which can be made with chicken, fish or pork. The chilli paste can be bought, but it will never be as good as one you have made yourself. Crushing the lime leaves in your hand releases the oils (smell your hand afterwards; it is the most divine aroma). If you want to make the soup more substantial, add 200 g blanched egg noodles.