25g/1oz/2 tbsp butter
450g/1lb butterhead (romaine) lettuce leaves, shredded
1 large bunch of spring onions (scallions), chopped
1 tbsp plain (all-purpose) flour
600ml/1 pint/2½ cups vegetable stock
150ml/¼ pint/scant ⅔ cup milk
salt and ground black pepper
1 Melt the butter in a pan, add the lettuce and spring onions and cook gently for 10 minutes until softened.
2 Stir in the flour and cook, stirring, for 1 minute. Add the stock and bring to the boil. Reducethe heat, cover the pan and simmer for 45 minutes.
3 Allow the soup to cool a little, then blitz in batches in a blender or food processor until smooth. Return to the pan and stir in the milk. Reheat and season to taste. Serve the soup in warmed bowls.