Place the parsnip and potato in the slow cooker with the apple, onion and garlic. Stir in the stock and saffron threads. Cover and cook on high for 4 hours.
Purée the mixture until smooth, using a stick blender, food processor or blender. Season to taste with sea salt, then stir in the cream. Cover and cook for a further 20 minutes.
Ladle into bowls and serve sprinkled with chiv