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.