Preheat the oven to 325 degrees. Season lamb all over with salt and pepper. Heat 2 tablespoons oil in a large Dutch oven over high heat. Add lamb shoulder, and cook, turning occasionally, until lamb is browned all over, 8 to 10 minutes. Remove lamb; set aside. Pour out any excess oil, and discard. Add remaining tablespoon oil and heat over medium-high heat. Stir in garlic, celery, carrot, onion, herbs, nutmeg, and cloves. Season with salt and pepper. Cook for 1 minute. Return lamb to Dutch oven. Add wine and tomatoes. Bring to a boil, cover, and transfer to the oven. Cook until fork-tender, 2 1/2 to 3 hours.
Remove from oven. Transfer lamb to a platter, and keep warm. Make sauce: Place the Dutch oven over low heat, and cook the liquid until it has reduced and thickened, about 3 minutes. Remove twine from lamb, and slice; serve with sauce.