Clean and wash the watercress and, except for something to garnish, chop coarsely. Peel and finely chop the onion
Heat the fat in a saucepan. Sauté the onion in it. Dust with flour and sauté. Stir in milk, a good 1/2 l water and stock. Bring to the boil and simmer for about 5 minutes
Roast pine nuts without fat until golden brown, remove. Fry ham in a pan until crispy. Take out and break roughly. Stir the watercress into the soup. Puree finely with a chopping stick. Season to taste with salt and pepper. Serve the soup with 1 teaspoon crème fraîche. Garnish with ham chips, pine nuts and the rest of the watercress