Leg of Lamb with Tangerine Sauce

1 (6 to 9 pound) leg of lamb, bone in
    or 1 (5 to 7 pound) boneless, rolled and tied
2 cloves garlic, cut into slivers
Vegetable oil
1 teaspoon rosemary
Salt
Ground pepper
1 1/2 cups tangerine juice
1/2 cup Grand Marnier
1/2 cup apricot jam
2 tablespoons cornstarch
1/2 teaspoon dried mint
1/4 teaspoon ground ginger (optional)

Preheat oven to 325 degrees F.

In shallow roasting pan, place lamb, fat side up. With sharp knife, cut slits in lamb. Insert garlic slivers in slits. Roast lamb at 325 degrees F for 20 to 25 minutes per pound when using a bone in leg (25 to 30 minutes, if using a boneless leg), or until meat thermometer placed in thickest part of meat reaches 140 degrees F for rare or 150 degrees F to 155 degrees F for medium. Allow lamb to stand in a warm place for 15 to 20 minutes before carving.

Meanwhile, in medium saucepan, combine remaining ingredients. Simmer, stirring constantly, until thickened. Serve with leg of lamb.