- 6 cloves of garlic (1 split, the rest chopped)
- 2 pounds russet potatoes, peeled and very thinly sliced
- Salt and black pepper, to taste
- 1 tablespoon fresh thyme
- 2 large onions, very thinly sliced
- 5 medium-sized tomatoes (about 1 pound), cored and thinly sliced
- 2/3 cup dry white wine
- 1/3 cup olive oil
- 1 leg of lamb, with bone in (about 6 to 7 pounds)
- Preheat the oven to 400°F. Rub the bottom of a large (16x10x2-inch) gratin dish with the split garlic clove. Arrange the potatoes in a single layer. Season with salt, pepper and some of the thyme and chopped garlic. Layer the sliced onions on top; repeat the seasonings. Layer the tomatoes on top and season with salt, pepper and remaining garlic and thyme. Drizzle the top with the wine and then the oil.
- Trim the thicker portions of fat from the leg of lamb. Season the meat with salt and pepper. Place the lamb on a sturdy cake or oven rack directly on top of the gratin dish.
- Roast, uncovered, for about 1 hour and 15 minutes for rare lamb. (For well-done, roast 30-40 minutes more.) Turn lamb every 15 minutes, basting with liquid from the dish underneath. Remove from the oven and let the lamb sit for 20 minutes before carving.
- To serve, carve the lamb into thin slices and arrange on a serving platter, with the vegetable gratin alongside.