Dry the lamb with paper towels and place on a rack in a heavy roasting pan.
In a small bowl, combine all the glaze ingredients; mix well.
Spoon the glaze evenly over the lamb; pour 2 cups water into the pan.
Roast the lamb for 1/2 to 1 3/4 hours, or until an instant-read thermometer inserted in the thickest part of the lamb reads 135° for medium-rare (check periodically to make sure there is some liquid in the bottom of the pan and add more water if necessary).
If you prefer lamb more well don, cook to 140° to 150° for medium.
Remove the lamb and place on a carving board; let rest for at least 10 minutes.
Place the roasting pan on top of the stove and add a bit more water; cook over medium heat, stirring to scrape up the browned bits from the bottom of the pan.
Taste and adjust the seasonings; degrease the pan juices and pour into a gravy boat.
Care the lamb into thin slices and serve with the juices.