Roast Mint Lamb

1 cup white cr?me de menthe liqueur
1 cup finely chopped onion
2 cloves garlic, minced
1 teaspoon salt
1/4 teaspoon pepper or more
1 ( 5 to 6 pound) leg of lamb
1 cup heavy cream
2 tablespoons butter or margarine
2 teaspoons cornstarch
2 tablespoons water
Salt and pepper to taste

In bowl combine cr?me de menthe, onion, garlic, salt and pepper. Pierce lamb with skewer so marinade will penetrate. Place lamb in shallow dish or large plastic bag. Pour in marinade and refrigerate for 12 to 24 hours, turning meat often.

Drain and reserve marinade. Place lamb in shallow roasting pan. Roast at 325 degrees F for 1 1/2 to 2 hours or until meat thermometer registers 140 degrees F for rare. 160 degrees F for medium and 170 degrees F for well done. Baste often with marinade. (Add water to roasting pan if dry). Remove lamb to heated serving platter. Scrape pan juices into a medium saucepan; add 1/2 cup reserve marinade, cream and butter. Combine cornstarch and water, add to saucepan. Cook, stirring constantly until mixture boils and thickens. Season to taste.

Serve sauce with lamb.