Courgette Soup with Watercress and Pecorino Pesto

Begin by melting the butter gently in a large saucepan, add the potatoes, courgettes, onion and garlic and stir everything around so the vegetables are glossy and covered in butter.

You can also watch how to chop onions and prepare garlic in our Cookery School Videos on this page.

Add a little salt and freshly milled black pepper, then partially cover the pan and leave the vegetables to sweat, to release the buttery juices, on a low heat for 15 minutes. Now add the stock, bring the soup back to simmering point and cook very gently for a further 7-10 minutes, again partially covered, or until the potatoes are soft and the courgettes are just tender.

While the soup is simmering, make the pesto. All you do is put the watercress (stalks and all), garlic, pine nuts and olive oil, together with some salt, in a food processor or blender and whiz until you have a smooth purée. Then transfer the purée to a bowl and stir in the grated Pecorino (or Parmesan - but not for a vegetarian) cheese. 

When the soup is ready, cool it a little, then purée it in a blender until smooth – you will probably need to do this in two batches, so have a large bowl nearby to pour the first batch into. 

Next, put the whole lot back in the saucepan, stir in the cream, then gently re-heat the soup.

Ladle it into bowls, top each one with a spoonful of the pesto and, using a skewer or the tip of a small knife, zigzag the pesto all over the surface of the soup.