Creamy Spinach Soup

1 large onion, coarsely chopped
6 cups water
3 potatoes, peeled and chopped
3 zucchini, thickly sliced
2 cups tightly packed washed and dried fresh spinach leaves
Several twists of freshly ground pepper
1/4 package (3.5 ounces) enoki mushrooms (optional)
Place the onion in a large pot with 1/2 cup of the water. Cook and stir
until the onion softens slightly, about 3 minutes. Add the remaining water
and the potatoes, zucchini, and soy sause. Bring to a boil, reduce the
heat, cover, and simmer for 35 minutes. Add the spinach and pepper. Cook
for another 2 minutes. Remove from the heat. Puree the soup in batches in
a blender and return to the pan. Add the mushrooms, if desired. Heat
gently for 5 minutes. Serve hot.
This is how the recipe appears in the book. I have noted some additions
from a posting here on the FF list to use 2 bunches of fresh spinach, and to
add cayenne pepper and garlic powder to taste.