1 (5 1/2-lb) piece boneless butterflied leg of lamb
1 1/2 tablespoons kosher salt
1 teaspoon finely chopped fresh rosemary
1 tablespoon Maldon sea salt or other flaky sea salt
Special equipment: 8 to 10 (12-inch) wooden or metal skewers; an instant-read thermometer
Directions
Stir together yogurt, garlic, rosemary, and pepper in a 13- by 9-inch glass baking dish or 2-gallon sealable plastic bag. Add lamb, turning to coat completely, and marinate, covered and chilled, turning over once or twice, 5 hours.
Bring lamb to room temperature, about 1 hour.
Remove lamb from marinade, discarding marinade, and put on a work surface. Run skewers horizontally through meat, about 1 1/2 inches apart, first lengthwise (4 or 5 skewers), then crosswise (4 or 5 more) to form a grid. (Skewering makes meat easier to move and turn over.) Sprinkle with kosher salt.
Prepare grill for cooking. If using a charcoal grill, open vents on bottom of grill, then light charcoal. Charcoal fire is medium-hot when you can hold your hand 5 inches above rack for 3 to 4 seconds. If using a gas grill, preheat burners on high, covered, 10 minutes, then reduce to moderate.
Grill lamb, covered only if using a gas grill, on lightly oiled grill rack, turning occasionally, until thermometer inserted diagonally into thickest part of meat registers 125°F for medium-rare (thinner parts will register higher), 25 to 30 minutes if using charcoal or 20 to 25 minutes if using gas. Transfer lamb to a cutting board and let stand 10 minutes before thinly slicing.
Stir together rosemary and sea salt and serve with lamb.
