Remove the tough stalks from the watercress, Rinse it under plenty of cold running water and put it in a casserole.
Cover and microwave on HIGH for 2 minutes.
Drain the watercress in a strainer (sieve).
Put the frozen creamed broccoli in a dish and microwave, uncovered, for 4 minutes on HIGH.
Rinse the whiting fillets under plenty of cold running water and pat dry on kitchen paper.
Puree in a food processor for 1 minute.
Add the watercress, salt and pepper.
Puree again.
Beat two of the eggs with a fork.
Add 1/4 cup (3 tablespoons) of sour cream (creme fraiche), beating constantly.
Season with salt and pepper.
Add the whiting and watercress puree and the broccoli.
Taste and adjust seasoning.
Butter the base and sides of a small Pyrex ring mold (mould) and pour in the mixture.
Cover and microwave on HIGH for 10 minutes.
Put a serving dish upside down on the ring mold (mould) and turn it over.
Leave the mixture in the mold (mould) to stand for 3 minutes.
To make the sauce, mix together 1 egg, the remaining sour cream (creme fraiche) and the shrimp (prawns) in a bowl.
Season with salt and pepper.
Heat in the microwave oven for 1 minute on HIGH.
Remove the pyrex ring mold (mould) and drain off any liquid from the dish.
Put half the sauce in the middle of the whiting mousse and pour the rest into a sauceboat.