Heat oil in a deep saucepan and add leeks, onion, garlic and bayleaf. Sauté gently for 5 minutes, stirring occasionally. Add watercress and stir well. Add stock and bring to the boil, then turn to a simmer.
Mix lamb with half the mint, all the cornflour, salt and diced shallots. Mix well and roll into marble-sized balls. Add to soup and poach for 5 minutes. Stir in spinach and remaining mint, check seasoning and bring to the boil. As soon as it comes to the boil, take it off the heat and serve.
© 2003 Peter Gordon. All rights reserved.