Heat oven to 400° F. Rinse the chicken and pat it dry. Arrange the chicken, onion, and sweet potatoes in a 9-by-13-inch baking dish. Drizzle the oil over the chicken and vegetables and season with the salt and pepper. Toss to coat. Drizzle with the maple syrup and top with the sprigs of thyme.
Roast, stirring the vegetables once, until the chicken is cooked through, about 1 hour, 15 minutes. Let rest for 10 minutes before serving.
Tip: The maple glaze can also be used with a whole chicken or Cornish game hens.