Personally, I've always wondered how these western Anglo-Saxon cooks manage to get away with serving raw watercress. I mean - have you tasted the raw stuff?
In my experience, watercress makes a good soup. Pretty easily made too.
Watercress soup
Boil some water with some chicken/beef/pork bones (or use some soup stock).
After this stuff has simmered for a while, toss in a bunch of watercress that's been cleaned and cut to about 5-7cm length pieces. You need enough watercress to fill up the empty water space such that you can still stir the mixture (alternatively, you estimate the amount of water by working backwards from the amount of watercress you have). Toss in some garlic cloves and some peppercorns. A touch of soy sauce to taste.
Boil on low to medium heat for ... between 1/2 to 2 hours. If you toss in some meat together with the soup bones, this can be a complete meal taken with rice.
Relatively easy to make. The toughest bit is washing the watercress.