Peel the parsnip and cut into 2 cm pieces. Chop the shallots and finely chop the garlic.
Heat the butter in a soup pan and fry the parsnip, shallot, garlic, caraway seeds, pepper and salt (if necessary) for 5 min. over medium heat. Stir regularly. Add the boiling water and crumble the stock over it. Bring to the boil and leave to simmer for 10 min.
Remove the pan from the heat, add the mustard and puree the soup with the hand blender. Pour the soup into bowls, sprinkle with cress and pepper.