Place shiitake and maitake in separate bowls, cover with warm water and soak 20 minutes. Drain off soaking water and reserve 2 cups. Chop the maitake and shiitake coarsely.
Heat oil in a soup pot and sauté the onions and garlic for 3 minutes. Add celery, potatoes and sauté 2 minutes. Add water, mushroom soaking liquid, kombu and sea salt to the pot. Cover and simmer over a low flame for 5 minutes. Remove kombu and discard. Cover and simmer another 15 minutes. In two batches, puree in a blender until creamy. Place the liquid puree back into the pot. Add all remaining ingredients, except the parsley and chives and simmer on low without boiling until hot. Turn off flame, mix in parsley and chives. Mix and serve hot or chilled.
7g fat (33% calories from fat),