Chilled Watercress Vichyssoise

15 g/1/2 oz polyunsaturated margarine
1 large onion, peeled and chopped 225 g/8 oz leeks, trimmed and sliced 350 g/12 oz potatoes, peeled and diced
1 litre pints vegetable stock
grated rind of 1/2 lemon
salt
freshly ground black pepper
2 hunches watercress, trimmed 150 ml/1/2 pint skimmed milk

Melt the margarine in a large saucepan and cook the onion and leeks gently for 5 minutes, stirring constantly. Add the potatoes to the pan and pour in the stock with the lemon rind, and salt and pepper. Cover the pan and bring to the boil. Simmer for 30 minutes until the vegetables are tender.

Reserve a few sprigs of watercress and coarsely chop the rest. Add the chopped watercress to the pan and simmer for 2 minutes.

Liquidize to a smooth puree. Stir in the milk, then taste and adjust the seasoning. Chill well before serving. Garnish with the reserved cress. SERVES 6