Sweet Potato Soup

1 tablespoon vegetable oil
1 cup chopped onion
1/2 cup chopped celery
2 teaspoons minced, peeled, fresh ginger
1/4 teaspoon dried thyme
1/8 teaspoon saffron threads
6 cups chopped peeled sweet potato (about 2 pounds)
1 tablespoon grated orange rind
7 1/2 cups vegetable broth
1/8 teaspoon ground red pepper
2 cups chopped spinach

Heat oil in a large Dutch oven over medium-high heat.
Add chopped onion, celery, minced ginger, dried thyme, and saffron threads, and saute 5 minutes.
Add sweet potato and orange rind, and saute 3 minutes.
Add broth and red pepper, and bring to a boil. Cover, reduce heat, and simmer 25 minutes or until potato is tender.
Place half of potato mixture in a blender or food processor, and process until smooth. Pour pureed mixture into a bowl. Repeat procedure with remaining potato mixture.
Return pureed mixture to pan. Stir in the spinach, and cook until thoroughly heated.

Yield: about 1/2 gallon