If you live near a river or stream, it's likely that you will have wild watercress growing on the banks. While there, you may also find freshwater crayfish in the river itself which can be caught using a net or pot.
The beauty of this soup is that it works equally well served hot or cold.
250g watercress, rinsed
1 leek, rinsed, trimmed, roughly chopped
1tbsp rapeseed oil
½tbsp plain flour
1 litre vegetable stock
Sea salt and freshly ground black pepper
16 preferably live freshwater crayfish
1tbsp fennel seeds
Cut the stalks from the watercress and put the leaves to one side. Gently cook the leek in the vegetable oil in a covered pan until soft, without allowing it to colour. Stir in the flour, then gradually add the vegetable stock, season with salt and pepper and bring to the boil. Simmer for 10 minutes, then add the watercress stalks and simmer for another 5 minutes.
Remove from the heat, add two-thirds of the watercress leaves and blend the soup in a liquidiser until smooth. Strain through a fine-meshed sieve, not too fine as it becomes watery. Bring back to the boil briefly and season again with salt and pepper.
If you are planning to serve the dish chilled, then cool it down on some ice first before refrigerating.
To cook the crayfish, bring a pan of heavily salted water to the boil with the fennel seeds and simmer for 5 minutes. Drop in the crayfish, simmer for 3-4 minutes, then drain in a colander and leave to cool.
Remove the tail meat by pulling away the heads and squeezing the shells until they crack, then carefully peel them. If the claws are large you can crack them with the back of a heavy knife. Next, add the crayfish meat to the soup and serve.