What you will need:
What to do:
Coarsely chop onions to measure 1 cup. Slice washed leeks lengthwise, thinly. Pour the olive oil into a pot. Add garlic, onions and leeks. Sauté over low heat until very tender.
Add potatoes, peeled and sliced, salt and 2 ½ cups of water. Cover and simmer until potatoes are almost done.
Remove thickest stems from a bunch watercress, chop coarsely, reserving a few sprigs. Set aside.
Add milk and 1 ½ cups of water to soup and bring to a boil. Add watercress and cook one minute longer. Puree in food processor or blender.
Serve hot or cold, garnished with reserved cress sprigs and snipped scallions or chives.