Preheat oven to 400 degrees. Halve yams, and place, cut side up, in a shallow baking dish just large enough to hold them in a single layer. Drizzle with oil, and sprinkle with thyme. Season with salt and pepper. Bake until golden brown and very tender, 35 to 45 minutes.
Lovely. Add more thyme than the recipe suggests. Use half of the thyme at the beginning and add the remainder 5-10 minutes before the potatoes complete their roasting time. This way some of the thyme will be deliciously seared, but not all.