This is very refreshing on a hot summer lunch, like today. We have not really had many yet here in Victoria, BC. this year.
Start by rubbing a split garlic clove at the bottom of a small pot, then turn the heat on medium low to slowly saute a sliced onion in butter with one tsp olive oil until golden. The slower the better, the taste will be both stronger and sweeter.
In another pot, boil a peeled potato cut in quarters 8 minutes in two cup broth, add two bunches watercress minus 2 inches cut off at the base and cook till the potato is well done. The lid should be on the pot.
Mix the two pots’ contents in the blender and pulse until very fine. Add one and half cup buttermilk. Chill one hour.
Hot version: add 1/2 cup cream and more broth, no buttermilk.