Heat the oil in a large pan and add the onions, celery, carrot and garlic. Cover the pan and
cook over a low heat for 45 minutes, or until the vegetables are soft, stirring occasionally to
prevent the vegetables sticking.
Add the peas and stock to the pan and bring to the boil. Reduce the heat, add the basil and
seasoning, then simmer for 10 minutes.
Spoon the soup into a food processor or blender and process until the soup is smooth. Return the
soup to the rinsed pan and reheat gently until piping hot. Ladle into warm bowls, sprinkle with
shaved Parmesan and garnish with basil.