How to Make It
Remove giblets from chicken; discard or reserve for another use. Season chicken all over with 4 teaspoons salt and 11/2 teaspoons pepper, making sure to season the cavity. Stuff cavity with shallot and thyme sprigs. Let stand at room temperature 30 minutes. Meanwhile, fill lid of a 4.1-quart Römertopf clay baker with water; let stand 30 minutes to allow water to soak into lid.
Toss together sweet potatoes, Yukon Gold potatoes, carrots, parsnip, garlic, chopped thyme leaves, remaining 1 teaspoon salt, and remaining 1/2 teaspoon pepper in bottom half of clay baker. Place chicken on top of potato mixture, and tuck wing tips under chicken.
Drain soaking water from lid. Cover chicken with lid, and place in lower third of a cold oven. Set oven temperature to 425°F, and bake until a thermometer inserted into thickest portion of breast registers 125°F, 45 to 55 minutes. Remove lid, and continue baking at 425°F until a thermometer inserted into thickest portion of breast registers 155°F, 20 to 30 more minutes. Let rest 15 minutes before carving. (Temperature will continue to rise to 165°F as chicken rests.) Serve chicken with vegetables.