Trim excess fat from the lamb and cut into even-sized pieces if necessary. Mix sumac, salt, black pepper, and minced garlic in a small bowl. Rub the spice mixture evenly all over the lamb pieces, coating thoroughly. Cover and marinate in the refrigerator for at least 10 minutes to allow flavors to penetrate.
2 tablespoons olive oil, 2 tablespoons sumac, 1 teaspoon salt, 0.5 teaspoon black pepper, 1 clove garlic
Preheat the oven to 400°F (200°C) or prepare a grill for high heat. Heat a tablespoon of olive oil in a skillet over medium-high heat until shimmering and slightly smoking. Place the lamb pieces into the hot skillet, searing each side for about 3-4 minutes until deep golden brown and a flavorful crust forms. Use tongs to turn the meat, ensuring even browning.
2 tablespoons olive oil
Once seared, transfer the lamb to a baking sheet if roasting, or keep on the grill grates if grilling. Insert a cooking thermometer into the thickest part of a piece. Roast in the oven or finish on the grill until the internal temperature reaches 135°F (57°C) for medium rare, about 15-20 minutes. Look for juices running clear and a slight firm texture when pressed.
Remove the lamb from heat and tent with foil. Allow it to rest for 5 minutes; this helps the juices redistribute and results in a tender, moist interior. During resting, the internal temperature will rise slightly to a perfect medium rare.
Slice the rested lamb against the grain into thick, even pieces. Arrange on a serving platter, optionally drizzling with a little extra olive oil or a squeeze of lemon for added brightness. Serve immediately to enjoy the tender, aromatic meat with a flavorful crust.
