Grilled Leg of Lamb with Rosemary Salt

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.