It may look unassuming but this small plant with delicate leaves and wonderfully peppery flavour is a real powerhouse. Gram for gram, watercress contains more calcium than milk, as much vitamin C as oranges and more folate than bananas. It’s high in vitamin K and for people like myself with low iron levels, it has more absorbable iron than spinach. Combined with sweetness of pear, mighty walnuts and creamy and complex flavour of Stilton, this simple, speedy and nourishing soup will soon become your favourite. This recipe has been adapted from Magic Soup: Food for Health and Happiness by Nicole Pisani and Kate Adams. In order to retain that incredibly vivid green colour, the unique flavour and nutrition, the key is to add watercress during the last two minutes of cooking.