For the lamb:
- 1 4-pound boneless leg of lamb
- Olive oil
- 1 bulb garlic, chopped
- 1/4 cup rosemary, chopped
- Zest of 2 lemons
- Kosher salt and pepper
For the roasted potatoes and tomatoes:
- 6-7 large Russet potatoes (about 4 pounds), peeled and sliced 1/8-inch thick
- Olive oil, for liberal drizzling (about 1/2 cup)
- Salt and pepper
- 4 tablespoons rosemary, chopped
- 4 tablespoons butter
- 4 large onions or 6 small onions
- 1 bulb garlic, cloves cracked from skin and thinly sliced
- 1 1/2-2 cups grated Parmigiano Reggiano cheese, loosely packed
- 2 28-32 ounce cans San Marzano tomatoes, lightly drained
- A handful of basil leaves, torn
- Pre-heat the oven to 450°F with the rack placed in the center of the oven.
- Coat the lamb in olive oil and slather with the chopped garlic, rosemary and lemon zest. Lightly salt and aggressively season with black pepper.
- Roast to brown for 15 minutes, then reduce the heat to 325°F and roast for 1 1/4 hours until a meat thermometer reads 130°F (for rare) or 1 1/2 hours until an internal temperature of 140°F for medium-rare once the meat has rested. Remove the net and thinly slice.
- While the lamb roasts, slice the potatoes, adding them to a bowl of salted cold water as you go. Once all of the potatoes are sliced, drain and add them to a large bowl. Dress lightly with olive oil; season with rosemary and pepper.
- Heat a large pan over medium heat with a drizzle of olive oil and melt the butter into it. Add the onions and garlic and season with salt and pepper. Cook until lightly golden and soft, 30 minutes, stirring frequently.
- Hand-crush the tomatoes and combine with the basil in a large bowl.
- Arrange a third of the potatoes in shingled layer in a large casserole dish. Sprinkle with a third of the cheese, top with half the onions, then layer in half the tomatoes. Repeat, topping the casserole with the last third of the potatoes and cheese. Place in the oven alongside the lamb at 325°F for 45 minutes. When you remove the lamb, transfer the potatoes to the upper third of oven and lightly broil to brown the cheese.