GETTING READY
1 Wash the watercress.
2 Drain well.
3 Take off all the leaves and their little stalks and discard all the thicker stalks.
4 Peel the shallots and chop very finely.

MAKING
5 In a pan, heat the stock.
6 In another pan, heat the butter.
7 Add in the shallots and fry for 3 minutes without browning.
8 Add in the watercress and a pinch salt, stir well.
9 Cover with a tight fitting lid, and allow to sweat over gentle heat for 5 minutes, or until the watercress has turned dark and wilted.
10 Sift the flour into the saucepan and stir well over low heat for 1 minute.
11 Remove from the heat.
12 Using a balloon whisk or wooden spoon, blend in the boiling hot stock, adding gradually to avoid any lumps.
13 Return to the heat, cover, and simmer for another 5 minutes.
14 Turn off the heat.
15 Use a hand held electric beater to beat the soup until it is very smooth.
16 Just before serving the soup, reheat it to boiling point and remove from the heat.
17 In a small bowl, beat the egg yolks with the cream.
18 Whisk into the soup.
19 Place over very low heat and continue beating for 2 minutes as the soup thickens a little.
20 Do not allow to boil or else the eggs will curdle.
21 Remove from the heat, and add a little more salt.

SERVING
22 Ladle the soup into heated soup bowls and serve.