3 medium leeks
3 medium parsnips, peeled and cut crosswise into ½-inch pieces
3 medium carrots, peeled and cut crosswise into ½-inch pieces
1 (2-pound) butternut squash, or any type of winter squash, peeled and cut into ½-inch cubes
2 large or 3 medium celery stalks, cut crosswise into ½-inch pieces
1 medium celery root, peeled and cut into ½-inch cubes
2 shallots, peeled and quartered
8 garlic cloves, thinly sliced
1 ½ tablespoons chopped fresh thyme leaves, or 2 teaspoons dried
3 tablespoons olive oil
Freshly ground black pepper
5 cups vegetable stock
¾ cup dry white wine
Position rack in the middle of the oven and preheat to 400°F.
Trim off the dark green sections from the leeks and save for making vegetable stock. Halve the pale green and white sections lengthwise. Rinse under cold running water, pat dry, and cut crosswise into ½ -inch pieces.
In one large or two medium very shallow roasting pan(s) or rimmed baking sheet(s), combine leeks, parsnips, carrots, squash, celery, celery root, shallot, garlic, and thyme. Drizzle with the olive oil, season with salt and pepper, and toss to evenly coat the vegetables. You don’t want to have vegetables on top of one another; you want them in a single layer.
Roast the vegetables for 20 minutes. Turn the oven temperature to 450°F and roast for another 10 minutes, or until the vegetables are a nice golden-brown, almost crispy on the edges, and almost soft when you gently test them with a fork or small, sharp knife. You don’t want them soft and mushy; they will continue cooking in the soup.
Meanwhile, in a large stockpot over high heat, bring the vegetable stock to a boil. Turn the heat to medium-low and gently simmer.
Remove the vegetables from the oven, add the wine and deglaze the pan, using a spatula to loosen any bits clinging to the bottom. Pour everything from the baking sheet into the stock. Turn the heat to low and simmer partially covered for 20 to 30 minutes. Taste and adjust the seasoning, adding more salt and pepper if needed.
Ladle the soup into mugs or bowls and serve hot.
Leftovers can be stored in an airtight container in the refrigerator for up to 5 days.