Watercress Soup

1/4 cup butter
1 bunch watercress
2 cups onion, thinly sliced
3 1⁄2 T. milk or cream
1⁄2 pound of potatoes, thinly sliced
salt and pepper to taste
2 1⁄2 cups stock
pinch of nutmeg

Melt butter and cook onions until soft. Add potatoes, seasonings and stock. Bring to a boil, simmer 15-20 min. Add watercress and simmer 5-10 min. For a creamy soup, cool mixture and process in a blender, stir in milk and heat, being careful not to boil.