Pat lamb dry and score fat by making shallow cuts all over with tip of a sharp small knife.
Pound garlic to a paste with sea salt using a mortar and pestle (or mince and mash with a heavy knife) and stir together with rosemary and pepper. Put lamb in a lightly oiled roasting pan, then rub paste all over lamb. Let stand at room temperature 30 minutes.
Preheat oven to 350°F.
Roast lamb in middle of oven until an instant-read thermometer inserted 2 inches into thickest part of meat (do not touch bone) registers 130°F, 1½ to 1¾ hours. Transfer to a cutting board and let stand 15 to 25 minutes (internal temperature will rise to about 140°F for medium-rare).
Add wine to pan and deglaze by boiling over moderately high heat, stirring and scraping up brown bits, 1 minute. Season pan juices with salt and pepper and serve with lamb.