Add oil, then turkey (skin side up) to a Dutch oven or roasting pan. Sprinkle with salt and pepper. Bake in a pre-heated 450 degree oven for 25 minutes, until skin is crisp. Add onion, garlic, basil, thyme, and broth. Cover and simmer over low heat or bake at 375 degrees about 30 minutes until turkey is nearly tender. Add potatoes and carrots. Cook about 20 minutes until vegetables are tender. Mix cornstarch and cold water and stir into hot mixture. Cook, stirring, until sauce is thickened.