1 Remove roots from leeks and cut away the dark green sections. Slice leeks and rinse carefully in cold water to remove any dirt and grit. Heat butter in a large heavy-based saucepan, add leeks and cook on low, stirring, for 5 minutes until leeks are soft; make sure they do not brown.

2 Add peas and lettuce to pan and cook, stirring, for 2 minutes. Pour stock and water into pan, stir to combine, then bring to a simmer and cook for 3 minutes. Season with salt and pepper. 

3 Purée soup using a stick blender in the saucepan (heat off) or in a large jug or bowl, or purée in small batches in a food processor. Return soup to saucepan and stir over a low heat until heated through. Ladle the soup into bowls and swirl in cream. Serve immediately.