This homemade vegetable stock from chef Sam Beall's "The Blackberry Farm Cookbook" is used to make his 10-Hour Braised Lamb.
Preheat oven to 400 degrees. Place onions, leeks, celery, parsnips, turnips, garlic, and mushrooms in a large roasting pan. Drizzle with olive oil and toss to coat. Transfer to oven and roast, stirring occasionally, until vegetables are lightly browned, about 45 minutes.
Transfer vegetables to a large stockpot. Add 2 cups water to roasting pan and scrape up browned bits from bottom of pan; pour into stockpot. Add 10 cups water to stockpot, along with parsley, thyme, bay leaf, peppercorns, wine, and salt. Bring to a boil over high heat, then reduce heat to low. Partially cover pot and gently simmer stock until vegetables are very soft, 30 to 45 minutes.
Strain stock through a fine-mesh sieve into a large bowl; discard solids. Stir vinegar into stock and use immediately or cool to room temperature and transfer to an airtight container. Refrigerate for up to 3 days or freeze for up to 2 months.