1. Melt vegan butter in a heavy-bottomed saute pan. When it foams, add the potatoes and onions; toss until well coated. Sprinkle with salt and freshly ground pepper.
2. Cover the pan and sweat the vegetables over low heat for 10 minutes. Add the stock and "milk," bring to a boil and cook until the potatoes and onions are soft.
3. Add the watercress and boil with the lid off for approximately 4-5 minutes, until the watercress is cooked. It will taste soft and tender. Do not overcook, or the soup will lose its fresh green color.
4. Puree the soup in a blender or food processor (I used an immersion blender). As with all soups, if you use a blender be sure to let it cool a little first or it may explode hot soup on you, due to the pressure that is created!
5. Divide among 6 soup bowls and serve immediately. Optionally, garnish with a swirl of nondairy sour cream.
Enjoy!
Source of recipe: This recipe is a very simple compilation of many recipes I found on the internet for watercress soup. The main inspiration was a recipe I found that is originally from Chef Darina Allen of Ballymaloe Cooking School in Ireland.