In a small bowl, combine the thyme, parsley and rosemary. Using a sharp knife, score the entire surface of the ham in a crosshatch pattern, cutting down just through the skin to the flesh underneath. Rub the outside of the ham all over with the herb mixture, pressing it gently into the crosshatch spaces between the skin. Sprinkle the ham with salt and pepper. Set aside to marinate and come to room temperature, 45 to 60 minutes.
Preheat the oven to 350 degrees F.
Place the herb-crusted ham in a roasting pan. Bake until the internal temperature reaches 150 degrees F on an instant-read thermometer inserted near the bone, approximately 25 minutes per pound, or 2 1/2 to 3 1/2 hours. Remove from the oven to a rack. Tent the ham loosely with aluminum foil and let stand until the center of the ham registers 155 degrees to 160 degrees F on the instant-read thermometer, 25 to 30 minutes.
Transfer to a cutting board and carve. Serve with roasted sweet potatoes.
Recipe courtesy of Virginia Willis