I double this recipe for Thanksgiving:
6 tablespoons olive oil
2 tablespoons chopped fresh thyme
2 tablespoons chopped fresh marjoram
2 pounds sweet potatoes, peeled, halved lengthwise, then cut crosswise into 1¼" to 1½" pieces
1½ pounds carrots, peeled, cut into ¾"-thick rounds
1½ pounds parsnips, peeled, cut into ¾"-thick rounds
1½ pounds rutabagas, peeled, cut into ½" pieces
1 pound red onions, peeled, root ends left intact, cut into ½"-thick wedges
Heat the oven to 425°. Spray two large rimmed baking sheets with nonstick spray.
Whisk the oil, thyme, and marjoram in a large bowl. Add the veggies and toss to coat. Sprinkle generously with sea salt and pepper and divide between the prepared baking sheets. Roast until tender and brown in spots, turning occasionally, about 50 minutes. (Can be made 4 hours ahead. Let stand at room temperature. If desired, rewarm in 350° oven about 15 minutes.) Serve hot or at room temperature.
Update (11/23/07): This Thanksgiving, for the first time ever, I roasted half the veggies (that is, one entire recipe, since I always double it) on Wednesday and refrigerated them overnight. Then I roasted the second half on Thursday morning and reheated both batches together. It worked out fine and saved me an hour of precious oven-time on the Big Day.