Gently fry onion and garlic in a small amount of butter until transparent.
Season lightly with salt and pepper, and add water and potato and boil until soft.
Pick over watercress and chop 4 or five sprigs and set them aside.
Purae the onion mixture in a blender.
Add most of watercress, blend, re-season to taste and return to heat.
Bring mixture to boil and simmer for 2 or three minutes.
Stir gently to prevent soup from sticking to bottom.
Remove from heat.
This is the decision point.
Either set aside to cool, then chill, or carry on to serve the soup
hot.
Stir in cream and chopped watercress. Heap a teaspoon of caviar on each
of the water
biscuits and float one on each bowl of soup immediately prior to serving.
Notes
Use the minimum amount of butter, oil, or margarine that will turn the
onion transparent. Those
who are particularly diet-conscious could dispense with this step,
and with the cream. Don't
overdo the garlic, 1/2 a small clove is ample since it is a background
flavour, not one that you
should be aware of.
A caution regarding seasoning. Potatoes absorb a lot of salt so you
may find it undersalted. The
caviar on the other hand, is very salty. This, for me, is a delightful
and important contrast.
Guests can always add extra salt if they choose.