• 2 bunches watercress
• 450 g/1 lb potatoes
• 1 onion
• 25 g/1 oz butter
• 6 dl/1 pint chicken stock
• 3 dl/½ pint milk
• salt and freshly milled pepper
• 1.5 dl/¼ pint single cream

Thoroughly wash the watercress, dipping it head downwards in plenty of cold water. Set one bunch aside for the garnish. Cut away the stalks from the remaining bunch and then coarsely chop the leaves and top parts of the stalks. Peel and dice the potatoes. Peel and finely chop the onion.

Melt the butter in a large saucepan, add the onion and fry gently for a moment. Add the potatoes, chopped watercress, stock and milk. Season with salt and pepper and bring up to the boil. Simmer gently for 1 hour.

Meanwhile nip the leaves off the stalks from the reserved bunch of watercress and chop finely. Draw the soup off the heat and pass the vegetables and liquid through a vegetable mill or purée in a blender. Return to the pan and reheat. Stir in the cream and chopped watercress, check the seasoning and serve.