8 medium parsnips, peeled and cut into 2-inch lengths
4 large turnips, peeled and quartered
4 medium carrots, cut into 2-inch lengths
2 large leeks, halved lengthwise and cut crosswise into 1-inch pieces
2 1/2 cups chicken stock or canned low-sodium broth
1 thyme sprig
1/2 pound small purple or red-skinned potatoes
Preheat the oven to 350°. Put the shallots on a large piece of foil and top with 1/2 tablespoon of the butter. Season with salt and pepper and seal the shallots in the foil. Bake for about 30 minutes, or until tender.
In a large saucepan, combine the parsnips, turnips, carrots, leeks, chicken stock, thyme and the remaining 2 tablespoons of butter. Bring to a boil over moderately high heat, then reduce the heat to low and add a pinch each of salt and pepper. Cover and simmer, stirring occasionally, until the vegetables are tender, about 20 minutes. Discard the thyme sprig.
In a medium saucepan, cook the potatoes in boiling salted water until tender, about 10 minutes. Drain the potatoes and cut them into 2-inch cubes. Add the potatoes and roasted shallots to the vegetable stew, season with salt and pepper and serve.