Heat the oven to 400 degrees. Allow 5 to10 minutes for this before you begin the recipe. Trim all the vegetables except the shallots and garlic, leaving a little of any green tops. Scrub them clean with a pot scrubber in cold water, then dry them on a dish towel. In a 9 by 13-inch roasting pan heat the oil over medium heat, add the vegetables as you cut them. Quarter the carrots and the turnips; if using, cut the celery in 4 wedges, halving each wedge. Halve the beets and cut the potatoes in 2 to 3 pieces. Add the shallots and garlic in their skins. Mix sugar, nutmeg, allspice, walnuts, salt and pepper in a small bowl, sprinkle them over the vegetables and mix well. Cover with foil and roast the vegetables in the heated oven until they are tender and browned, 45 to 55 minutes. If you have time, stir them occasionally so they brown evenly. Alternatively, if using the microwave, transfer the vegetables and flavorings to a microwave dish and cover with wrap. Cook 8 minutes at high, stir and cook another 8 minutes. Stir again and cook uncovered 4 to 6 minutes until tender.