Directions: 1. Heat oven to 450 degrees. Combine oil, leeks, carrots, celery, parsnip, potatoes, garlic and mushrooms in a large roasting pan; stir to coat vegetables with oil. Roast, shaking pan occasionally and turning ingredients once or twice, until everything is nicely browned, about 45 minutes.
2. Use a slotted spoon to scoop all ingredients into a stockpot; add all remaining ingredients (except salt and pepper) and 8 cups water. Turn heat to high. Meanwhile, put roasting pan over a burner set to high, and add 2 to 4 cups water, depending on depth of pan. Bring it to a boil, and cook,
scraping off all bits of food on bottom. Pour this mixture into stockpot (along with 2 more cups of water if you used only 2 cups for deglazing).
3. Bring stockpot to a boil. Partly cover, and adjust heat so mixture sends up a few bubbles at a time. Cook until vegetables are very soft, 30 to 45 minutes. Strain, pressing on vegetables to force out as much juice as possible. Taste, and add more soy sauce, salt or pepper if necessary. Store or serve.