Carefully remove the pot from the slow cooker and use a hand-held blender to blitz the soup until smooth – watch out for splashes. Stir in enough milk to reach your preferred consistency (see Tips).
For a thicker soup, add 2–3 tablespoons cornflour mixed with a little water at the same time as the milk or cream. You will need a slow cooker that holds at least 4 litres/7 pints for this recipe.
Cover the slow cooker and turn to high. Cook on high for 3 hours, then mash a little using a potato masher. Serve immediately with fresh chopped parsley if you like a ‘chunky’ soup.